W203 CDI Battery charging

[nippynoo]

I need to recharge my flat battery on a 2006 W203 C220CDI. But I've read several scary posts (i.e.££££) about damage occurring to the electrics/SAM units when refitting batteries.

So I've decided to leave my battery where it is, and connected a 6-AMP charger directly across the terminals.

Battery voltage (with charger) is 11.90V and increasing very slowly. Is this procedure safe? I cant see why not.

 

[Grahamcol]

I don't want to alarm you unduly but I think with all modern(ish) Mercs and in particular with the W203 you have to be very careful about charging with the battery connected (as well as disconnecting it on the W203). My understanding is that you should only use an electronics safe charger such as a CTEK XS3600 or similar. Others will be along to assist you further, I expect.

 

[NISFAN]

Lead acid batteries don't like being as discharged as yours must be. There is a chance that it will never recover to a usable level, and therefore you will be putting the electronics at risk charging a duff battery.

Would have been better to use the right procedure to disconnect the battery to charge it and then test it, offline so to speak. If it is duff, you can then reverse the procedure and fit a new battery. You would need a spare 'donor' battery to do this safely.

 

[nippynoo]

Lead acid batteries don't like being as discharged as yours must be. There is a chance that it will never recover to a usable level, and therefore you will be putting the electronics at risk charging a duff battery.

I'm confused as to how any electronic damage can occur with a partially charged battery. Even if a fully discharged battery only recovers to 95% of previous full capacity, I can't see how a lower capacity can cause any electronic damage because the voltage to the electronics would be exactly the same. Someone please explain though...

Update: Well after 10 hours slowly charging my "in-situ" battery (still connected in the car) at 6-amps the voltage across the terminals has crept up slowly to 12.40V. Yesterday it was 11.5V. From a table published in another post , full charge corresponds to 12.70V. So I'll see if it gets there. Looks good so far though.

I'm just using a borrowed charger doesnt look cheap (its an ABSAAR Electronic Battery Charger and Analyser).

 

[NISFAN]

The biggest risk is when you connect or turn on the charger (voltage spike). As you have already done that, carry on

 

[nippynoo]

The biggest risk is when you connect or turn on the charger (voltage spike). As you have already done that, carry on

Yes I avoided any risk of spike by connecting the charger leads to the battery terminals before switching on at the mains. Never the other way around. This way the charger voltage has to build up from 0V, rather than drop down from spike voltage. I think this way is totally safe - or maybe I've just been lucky.

Battery is now fully charged