Bit of mega posting this one but hopefully it's a good reference for anyone experience battery draining problems.
Dominic,
Three cases of a discharged battery in a year suggests that you have an electrical or battery problem (unless you have been leaving it standing unused for a long time?)
Fault Diagnosis
Check the following in the order below (I am assuming you have no means of electrical testing):
Make sure the battery terminals and clamps are not corroded, if they are clean them with boiling water. Make sure the positive cable is not split or cracked which could lead to shorting out.
Undo the cell caps and inspect the cells. The electrolyte should be at the level indictated on the side of the battery, top up with distilled water if they are low. The electrolyte should be clear and not cloudly or dark. The plates inside should look even with no signs of bowing or bending. Feel the outside of the battery, if its bulging at all then the plates inside could be warped. If its bulging badly, a warped plate or blackened cell is evident then get a new battery! If the battery looks OK then check the other things on the list, if they are OK then suspect the battery then get it high-rate discharge tested (drop test) at an Auto Electrical store/supplier (Halfords should be able to do it) this will show up any faults.
Make sure the Alternator belt is tight enough and is not slipping.
From now on you will need electrical test equipment, if you don't have any then consult an Auto Electrician to do the tests for you.
Now the simple tests have been done it gets a bit more complicated. You need to do a 'battery current leakage' test. Basically this will test the amount of current being consumed when the ignition is off i.e. as if the car is parked up. All cars use a certain amount of battery current when the ignition is off, the dash mounted clock, alarm/immoboliser (even when not set), keyless entry system etc. all draw their own small amounts of current. It should only cause a problem if the current drawn gets excessive due to too many electrical devices fitted (that need current all the time) or if there is a fault draining the current.
You need a DC ammeter for this test capable of reading 0.01A (1mA) to 10A. With the car parked and ALL electrical equipment turned off (shut the doors!) disconnect the negative battery lead. Connect the positive lead of the ammeter to the negative battery lead and the other lead to the negative battery terminal. You should now get a reading of the battery leakage current. A reading between 0-0.03A means the current drain is acceptable. A reading over 0.05A means an excessive amount of current is being drained, certainly if you get over 0.1A then you have a definite problem! If you have found an excessive current leakage then you need to check where its coming from. The most common cause of current leakage in all cars is the boot light remaining on when the bootlids shut. Check this out by crawling in the boot and shutting it BUT make sure you have someone there who can get you out again! If that is not the problem then it is best to start pulling fuses and observing when the current drain drops, that way you can narrow down the circuit the problem is in.
I had a current drain problem in my old Mk1 MR2 which would flatten the battery over a weekend! I traced it to a faulty stereo head unit that was draining excessive current when everything was switched off. The stereo worked fine apart from this current drain! I took the stereo out and the car was perfect from then on.
If you find that there is no problem with excessive current drain then the last thing to check is the Alternator operation and the Voltage Regulator in the Alternator. If the regulator is faulty then it can be under charging the battery or over charging it (this will eventually damage the battery). To test the Alternator voltage output you will need a Voltmeter capable of reading between 12 and 17 Volts D.C. Make sure the battery is fully charged before starting the test. With the battery back on the car start the engine and let it idle. Make sure all electrical accessories are turned OFF. Connect the Voltmeter leads onto the battery terminals and rev the engine. Obverse the voltage reading over a wide rev range. The voltage should be between 13.5 to 15 volts although it may drop slightly at idle. Now turn on as many electrical items as you can (lights, heater or A/C, rear screen demist etc.). Again obverse the voltage reading over a wide rev range. The voltage should again remain between 13.5 to 15 volts although it may drop slightly at idle or just above idle. If the voltage drops below the 13.5 volts or goes above 15 volts then the Voltage Regulator or Alternator is faulty. Consult an Auto Electrician for repair.
If you have found the battery is faulty then see below for suggested replacements.
Suggested Battery Replacements For Evo's
There are 2 sizes of battery fitted to the Evo 4-6 the standard size battery is 44B20L or if you have a Cold Zone Specification car then you will have the larger 55B24L battery (its physically larger as well as larger capacity). I have noticed that the terminals are opposite ways around on these batteries. Either battery can be replaced with the following high power items (all comparisons stated against the OE battery refer to the 55B24L):
I have researched batteries for the E4-6 before and my findings are below (from a previous thread):
Lucas Supreme, Part Number 054/4
(SAE Cold Cranking Amp 335)
This is the same physical size as the OE battery however the terminals are the opposite way around so the battery has to be installed with the terminals near to the wheel arch as opposed to the front of the car. The terminals are the correct size and the bracket also fits OK around the slightly raised individual filler caps. Comes with a 4 year warranty.
Price from PDA(Farnham) £31.77 inc of VAT (available from any Lucas stockist)
Halfords, Part Number HB054
(SAE CCA 335)
This is a direct replacement for the OE item. As for the Lucas item above the terminals are the opposite way around so the battery has to be installed with the terminals near to the wheel arch as opposed to the front of the car. The bracket fits OK as the fillers are flush with the top of the battery. Comes with a 3 year warranty.
Price from Halfords (Farnham) £44.99 inc of VAT
Halfords, Part Number HB053
(SAE CCA 380)
This is the exactly the same size as the HB054 however the terminals are bigger and will require different terminations (positive terminal certainly, negative may be able to be altered to fit the battery). I am mentioning this one because it is a more powerful battery at CCA of 380 if you want to fiddle with the terminations. Comes with a 3 year warranty.
Price from Halfords (Farnham) £44.99 inc of VAT
The following WILL NOT FIT:
Halfords, Part Number HB015
Although it is roughly the same size as the OE item the bracket will not hold the battery as the fillers are in a raised unit on top of the battery stopping the bracket bar clamping down. I am mentioning this because some people have said in the past this battery will fit an Evo when in fact it won't!
I have fitted the Lucas item to my car after my OE battery (55B24L) became faulty after 8 months (1 cell was faultly). You will probably find that the manufacturers original battery on the car will not last as long as it should because it is usually been abused (siting around running down, recharging and jump starting etc. before the car is even sold!). Having said that the battery on my parents car was recently replaced for the first time since new and that had been on there for 10 years!
