battery loses charge

[sjp]

my merc 300e has no dash lights and a full battery will run down over night.but when you jump it it will run ok until you switch it off and try to restart it when nothing

 

[kiwi_bloke]

alternator?

if the batteries fine, give the alternator a look at

 

[kid-jensen]

sjp,

If you are SURE the battery's OK, it would need to be something pretty hefty to drain the power overnight.

Try pulling, say, 50% of the fuses and see if the problem goes away.

If it does, try putting 25% back......eventually you will localise the offending circuit.

As stated though, the first check should always be to see if it's charging. Check for at least 13 volts at 2000RPM with all the accesories on.

 

[Peter 300TE]

stupid comment maybe?

Check the battery cells are fully covered. We are all used to sealed batteries nowadays however this was a common problem once.

 

[GaryC]

Hello,

Have you try to check the Alturnator voltage and the battery voltage? when engine is running it should have about 13 to 14 volt, and the battery itself, when engine is off, it should have 11.5 to 12.

Also, please check the earth lead, which connect the alturnator to the engine and the chassis, I suffer this in my other car before....

Hope tgis could help...

Gary!

 

[Arnie]

How old is your battery? Are your sure it's OK. Try to charge it and then disconnect the ground (negative) cable overnight and see in the morning if it has retained its charge.

If so, then investigate the other items such as the alternator. However, it's output voltage really needs to be measured at it's terminal, not at the battery (also do not disconnect the battery while running as this may damage the alternator). If the iginition switch works properly, very few items should remain powered when it's switched off. Check interior lights, boot light etc. Also, does the car have an alarm.?...