Battery systems

Battery systems decide which machines your battery can power

What are battery systems? Battery, charger and machine from one brand, approved to work together. With us, that means FLEX at 12 and 18 volts and RUPES iBrid for the BigFoot cordless polishers. Same voltage doesn't mean same mount, though: the batteries of the two systems aren't interchangeable.

Battery systems are the power side behind your polisher, sander, heat gun and compressor. A battery system, also called a battery platform, is made up of battery packs, chargers and machines from one brand that are matched to each other. What they all have in common: the battery has to be approved for that exact machine. So when you pick a system, you're also deciding which machines you can add later without buying a new battery.

• One charger for two voltage classes. The FLEX CA 12/18 fast charger charges both the 12-volt and the 18-volt batteries. Within the 12-volt class, according to FLEX, every battery fits every 12-volt tool. So you only need one spot at the socket for both classes.
• Capacity costs weight on the machine. According to FLEX, the 18-volt battery weighs 0.42 kg at 2.5 Ah, 0.72 kg at 5.0 Ah and 1.06 kg for the 8.0 Ah version from the Power Plus range. The heavier the battery, the more you feel it in your wrist when polishing overhead or on a door panel.
• Genuine accessories protect the warranty. FLEX gives a three-year warranty on machines, batteries and chargers if you register within 30 days. For lithium-ion batteries, the terms limit the warranty to 700 charge cycles and require genuine accessories.

Detailing1's tip from the shop: A battery that spends the winter fully charged and plugged into the polisher is being stored against the manufacturer's advice. For longer breaks, FLEX recommends about 60 percent charge and storing the battery separately from the tool, dry and out of the sun. RUPES specifies 20 to 60 percent at around 20 degrees for iBrid batteries, with a top-up charge every six months. Take the battery out after your last polish of the season, don't charge it to full and put it in the cupboard.

A battery system is battery, charger and machine in one

A battery system ties one brand's battery packs, charger and machines together into a platform where every battery fits every approved tool in the same voltage class.

The benefit shows up straight away in detailing. In the FLEX system, the cordless polisher, the cordless random orbital sander before polishing, the cordless heat gun for film and the cordless compressor for tyres all run on the same 18-volt battery. You buy the power once and after that just the machine. That's why lots of machines are available as bare tools, listed in the shop as a version without battery and charger.

Technically, there's more in the battery than a few cells. FLEX talks about battery management with data exchange between tool, battery and charger, plus deep-discharge protection. Put simply: the electronics in the battery monitor the cells and cut out before a cell runs flat. What that means for you: if you run the machine until it stops, the cut-off protects the cells from deep discharge.

Voltage defines the class. FLEX has a 12-volt class for light work and an 18-volt class for heavy work. In the range, polishers, sanders, heat gun and cordless compressor run on 18 volts. The 12-volt batteries serve smaller tools, and the CA 12/18 charger charges both.

According to Google Trends, searches for battery systems peak each year in April. If you get into cordless polishing with your first machine in spring, you're also choosing your platform for the next few years.

Same voltage doesn't mean same mount

An 18-volt battery only fits machines its platform is approved for, because the mount, contacts and electronics are brand-specific — even when the voltage is identical.

In comments on cordless polishers, buyers explain their choice by the batteries they already own. If you already have batteries from one brand and buy a polisher from another, you end up with two systems on the shelf, two chargers and no battery that runs both machines. Stiftung Warentest calls system batteries practical but also criticises the lack of a cross-brand standard.

That exact boundary runs through our range. According to RUPES, the RUPES iBrid battery at 18 volts and 5 Ah is only approved for the BigFoot HLR15 and HLR21 iBrid machines and may only be charged in the RUPES dual charger. It doesn't fit FLEX machines, and a FLEX battery doesn't fit the RUPES machine. The smaller iBrid Nano tools also use their own 10.8-volt batteries.

There are cross-brand alliances like CAS, where several manufacturers share a common battery mount. They only apply to their members. So for your buying decision, what counts isn't the voltage on the label but the manufacturer's approval list for that exact tool.

Adapters and aftermarket batteries promise to get round this limit. The Power Tool Institute warns that third-party batteries and adapters can bypass the battery management that monitors cells and temperature in the original. So what you save on a knock-off, you pay for in safety that nobody has tested for your tool.

Capacity follows the continuous user, not the screwdriver

The right battery capacity depends on the machine that runs longest without a break — polisher, sander or heat gun — not on the smallest tool in the case.

Capacity is shown on the battery in amp hours, Ah for short. It describes how much charge the battery stores: a 5.0 Ah battery lasts about twice as long as a 2.5 Ah battery under the same load. Day to day, that means fewer swaps per car, but more weight on the machine.

Polisher, sander and heat gun draw power continuously as long as the trigger is pressed. A compressor works in bursts until it reaches the set pressure. FLEX doesn't say how many minutes a battery lasts on a particular machine. It depends on machine, pad, speed setting and pressure, which is why we don't quote runtime figures that aren't backed up.

Weight is the flip side. At 0.42 kg, the 2.5 Ah battery is the lightest; the 5.0 Ah battery comes in at 0.72 kg and, according to FLEX, the 8.0 Ah version from the Power Plus range at 1.06 kg. For spot repairs and small areas, the light battery does the job. For a full paint correction on a whole car, the 5.0 Ah battery carries the work with fewer interruptions.

One battery or two: your working day answers that. If you polish a whole car in one go, plan on two batteries so one charges while the other works. If you only do wheels or individual parts now and then, one battery is enough. You'll find the individual batteries and their capacities under Batteries.

If you already own a suitable charger, just buy the batteries and save yourself a second unit at the socket.

FLEX builds the 2.5 and 5.0 Ah batteries from 18650-format round cells; the newer 8.0 Ah XT battery uses larger 21700 cells with lower internal resistance. For you, that only matters as a side effect: lower internal resistance means less heat under load.

FLEX batteries only charge between 0 and 40 degrees

According to the manufacturer, you should only charge FLEX batteries between 0 and 40 degrees Celsius, and FLEX says to store them between minus 20 and plus 50 degrees Celsius.

The temperature limit isn't a formality. A battery that goes straight from a cold boot to the charger in winter should warm up to room temperature first. A battery that's hot after a long polishing session should cool down before it goes back on the charger. The electronics protect it, but they're no substitute for looking after it properly.

The upper storage limit mainly concerns the boot. A car standing in the sun in summer can get very hot inside. So the battery doesn't live in the car permanently — it comes into the house with you after the job.

On charging time, FLEX states that with the CA 12/18 fast charger a battery reaches about 80 percent after around 30 minutes. A double charger charges two batteries in parallel, but not faster per battery. You'll find the chargers in detail under Battery chargers.

The RUPES dual charger follows its own logic. With two batteries plugged in, according to RUPES it charges the fuller one first. In practice: the battery that's nearly done is the first one back on the machine. For the 5 Ah iBrid battery, RUPES quotes around 50 minutes of charging time.

Worn-out batteries don't go in household waste but to a collection point at a retailer or your local recycling centre. Tape over the terminals first so no contacts touch each other.

In our range, one battery powers several machines

The range is built around the FLEX 18-volt platform, supplemented by RUPES iBrid, and the FLEX cordless polishers come as a kit with exactly the battery and charger that are also sold separately.

The standalone battery is the FLEX "AP 18 V" Battery Pack (18V) in 2.5, 5.0 and 8.0 Ah. It pairs with the FLEX "CA 12/18 230/CEE" Battery Chargers (12/18V), which charges 12 and 18 volts. Together they're the basic kit every FLEX 18-volt machine runs on.

The cordless polishers show how the system is meant to work. The FLEX "PE 2 18-EC" Cordless Rotary Polisher Ø150mm (18V) and the FLEX "XFE 2 15 18-EC" 15mm Cordless Random Orbital Polisher, Free-Spin Ø150mm (18V) both come as a kit with two 5.0 Ah batteries and the CA 12/18, or as a version without battery and charger. The polishers themselves are under FLEX Polishers.

The cordless versions of the other machines run on the same 18-volt battery and are listed as bare tools. That goes for the cordless sanders under Sanders for sanding paint before polishing, the cordless heat gun under Heat guns for film and adhesive, and the cordless compressor under Compressors. The Cordless screwdriver isn't part of it: FLEX fits it with a built-in 4-volt battery that charges via USB-C.

The second world is RUPES. The Rupes BigFoot "HLR15" iBrid Cordless Random-Orbital Polisher Ø125mm is available as a kit with two 18-volt 5 Ah batteries and a charger. The spare battery and charger belong to the RUPES system, not the FLEX platform. There's more on the brand under Rupes.

You'll find every machine in this area, from polisher to compressor, together under Tools.

Aftermarket batteries put your warranty at risk

An aftermarket battery saves you money at the till but puts the manufacturer's warranty at risk, because FLEX requires genuine accessories for its three-year warranty and accepts no liability for third-party products.

Search for FLEX batteries and you'll see knock-off batteries labelled “for Flex 18V” right next to the originals. The price difference looks tempting until you weigh up the consequences: the warranty on machine, battery and charger depends on the genuine-accessories condition. Stiftung Warentest found individual cell monitoring in seven out of eight power tool batteries tested; for the knock-offs, there's no evidence of it.

A quick decision tree tells you which battery system fits. If you already own FLEX 18-volt batteries, buy your next machine as a bare tool. If you're new to cordless polishing, take the kit, because the batteries and charger come included. A RUPES iBrid machine needs RUPES batteries. For an overview of the brand, see FLEX Power Tools.

When you buy your first machine, the platform question feels bigger than it is. You're not committing to every machine for the next few years, just to the mount. You decide which machine comes next when the time comes, and the battery already in your cupboard makes that decision easier.

If you honestly only need one machine and have a socket within reach, you don't need a battery system. A corded polisher works without charging breaks and without battery weight. A battery system pays off as soon as you want to walk round the car without a cable or run several machines on the same battery.

From customer enquiries, we know the scenario where a missing charger stops the whole job even though machine and battery are ready to go. That's why the charger belongs in the plan from the start, not as an afterthought.

In the end, the battery is the investment and the machine is the add-on. Pick the platform right once, and you'll buy every further machine without battery and charger, because both are already in the cupboard. That's the real reason the choice of battery system comes before the choice of polisher.