The battery is part of your car that is essential yet rarely gets any maintenance or a second throught until it leaves you stuck and your car won’t start. Seeing as the early L series is rather sensitive to jump starting, as ECU’s are easily fried I thought I’d write a little about common faults that can lead to your battery becoming flat.
Battery keeps going flat
Is the battery charging?
With the engine running and a good battery, the voltage across the battery should be 13.5-14.5 volts.
Then switch on the headlights, heater, and heated rear window, the voltage should not drop below 13 volts.
If the voltage is not correct check the security and condition of the battery terminals, the main power and earth cables and the connections on them. Also check the security and condition of the alternator connectors. If voltage is still too high or low with the engine running then the alternator is faulty and needs overhauling or replacing.
Is something draining the battery?
If the battery is charging correctly but is still going flat when left stood it is likely that there is an electrical drain that is causing it to go flat. To test this you can connect an ammeter between the battery positive terminal and the battery positive lead. With nothing switched on in the car the current draw should be less than 0.1 amps. If it is higher than this then there is an electrical fault somewhere draining the battery. The most common causes are:
Faulty Alternator – If the diodes have failed in the alternator, although it may charge the battery correctly, when left the battery can discharge through it causing it to be flat in the morning. Clues are the alternator being warm even though the engine is cold. If the current draw falls when the alternator is disconnected or unplugged then this will confirm the alternator is at fault.
Chafed/faulty wiring in the boot hinge area – rover 200/25. This is a common problem point where the wiring passes from the roof into the boot lid at the hinge. This can cause all sorts of electrical faults including electrical drains. Peel back the rubber boot and repair any frayed or broken wires.
Incorrectly installed accessories – Items such as audio amplifiers and stereos should use an electrical feed that is turned on when the igntion is turned on. If they are wired incorrectly to a permenant electrical connection can cause a drain to occur.
Most batteries are low or zero maintenance, but if in doubt it is worth checking that the electrolyte level is correct in the battery cells. The level of electrolyte should be just above the level of the metal plates in the battery. Caution is needed as the battery contains acid! If the level is low in any of the cells top it up with de-ionised water, normal tap water shouldn’t be used. Any spills of acid from the battery must be immediately neutralised with lots of water and preferably washing soda.
Batteries naturally go flat over time so even if it is disconnected from any loads the battery will naturally flatten with time. This is why it is recommended to charge any battery in storage about once a month. If the battery has electrical loads placed on it, (alarm, immobiliser, clock, radio code etc), then the discharging is obviously more rapid and more regular charging may be necessary.