Battery & Electrical
The Car You Do Not Drive Enough
Five things that answer different questions about the same battery: is it charged, is it holding, is it finished, is something draining it, and will you bother.
Before you buy anythingThis page also considers Driving it once a fortnight, a solar maintainer on a car parked outside and Taking the battery out and indoors. Why, and when each is the better answer.
Contents
A battery in a car that gets driven is a solved problem. The alternator sees to it, and nobody thinks about it again until the battery is five years old.
A battery in a car that sits is a different object. It self-discharges, the car's own electronics keep drawing after everything is off, and the discharge does permanent damage that a later charge does not undo. The failure mode is specific and cruel: it is fine every time you check, and flat on the one morning you actually wanted the car.
The five things below are not five ways to charge a battery. Each answers a different question about the same battery — is it being kept charged, is it holding, is it finished, is something draining it, and will you actually bother. The last one is the reason most of these lists fail.
A note on this collection: these are chosen on which question each one answers, from published specifications and from how lead-acid batteries fail in storage — not from a winter of using them. See how we test.
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The maintainer — is it being kept charged
The item everything else is arranged around, and the one where the specifications matter least. Output current is nearly irrelevant for holding a healthy battery at rest; what matters is that it monitors and stops rather than pushing continuously.
NOCO GENIUS1 battery charger and maintainer
NOCO
Small output is correct for maintenance — this is not a fast charger and does not need to be. Check it is rated for the chemistry in the car, which matters if the battery is AGM rather than flooded.
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Against the other obvious choice, in CTEK MXS 5.0 vs NOCO GENIUS1.
The quick-connect lead — will you actually bother
The least impressive item here and the one that decides whether any of the rest happens.
A maintainer that requires opening the bonnet, finding the clamps and reaching over a wing is a maintainer used in November and forgotten in January. A permanently fitted lead ending in a connector somewhere reachable turns a five-minute job into a three-second one, and the difference in practice is whether it gets connected at all.
SAE quick-connect maintainer lead
Route it so the connector sits somewhere you can reach with the bonnet shut, and fuse it at the battery end. Check the connector matches your maintainer before buying — SAE is common but not universal.
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The monitor — is it holding
The maintainer reports nothing while it is unplugged, and the unplugged weeks are when the trouble starts.
A Bluetooth monitor sits on the terminals and logs voltage, so a battery falling away between visits becomes visible before it is a no-start. It is the difference between discovering a problem in the garage and discovering it on a morning you had plans.
12V Bluetooth battery monitor
Judge it on whether it logs history rather than only showing a live figure — a single reading tells you almost nothing, and the trend is the whole value.
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What a falling trend actually indicates is in a Bluetooth battery monitor and the drain warning.
The tester — is it finished
The hardest question of the five, and the one a voltmeter cannot answer.
A battery that has been left discharged sulphates, and a sulphated battery will take a charge, show a healthy resting voltage, and then fail the moment a starter motor asks it for real current. Voltage tells you state of charge; it says nothing about capacity. Only a load or conductance test separates "flat" from "finished".
ANCEL BA101 conductance battery tester
ANCEL
Conductance testers work on a battery that is charged, so charge it first or the reading describes the state rather than the health. Note the CCA rating printed on the battery before testing — the number is meaningless without it.
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The two kinds of test, and which answers what, in battery tester vs load tester.
The disconnect switch — is something draining it
For the car that sits longest, or sits where there is no power.
A modern car draws continuously with everything off, and on a vehicle stored for months that draw alone will flatten a healthy battery. A master switch removes the car from its own battery. It is the one item here that needs no electricity to work, which is exactly why it belongs on the list.
Battery disconnect / master switch
Check what the car loses when isolated: radio codes, alarm, seat and mirror memory, and on some cars the ECU adaptations. On a modern car that list is long enough to be the deciding factor.
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What was left out
A jump starter. Deliberately, and it is the most common purchase in this situation. A jump starter is what you buy instead of solving this — it recovers from the failure every time rather than preventing it once. It has a real place in a boot for a car you drive; it is the wrong answer for a car you do not. The comparison for that is Fanttik Potent T10 vs NOCO GB40.
A solar maintainer. The right answer for a car parked outside with no mains, and a genuinely different trade rather than a lesser version — see battery maintainer vs solar maintainer.
A second maintainer for a second car. Sensible if you have two stored cars, and it is a quantity decision rather than a different item.
Anything that claims to desulphate. The evidence for recovery pulses reversing established sulphation is weak and contested, and this site does not recommend on that basis. Testing the battery and replacing it if it fails is the answer that does not depend on a disputed mechanism.
The order to work through a car that will not start at all is the pillar, car electrical problems, in the order to check them.
If this is not right for you
- Driving it once a fortnight
- Free, and it solves the charge problem completely. It is also the thing people have already failed at, which is the honest reason the rest of this list exists.
- A solar maintainer on a car parked outside
- No mains needed, which is the whole argument where there is no socket. Slower and weather-dependent, and compared properly in the linked page below.
- Taking the battery out and indoors
- Works, costs nothing, and is genuinely correct for a car stored somewhere with no power. It also means losing the radio code and every seat memory.
Questions people actually ask
Is a trickle charger the same as a maintainer?
How flat is too flat to recover?
Do I need the disconnect switch if I have a maintainer?
Why bother with the monitor when the maintainer is already on?
Question this page did not answer? Ask it.