Battery drain advice please.

[trianglegirl]

Bought a second hand bongo and drove it home. Had to leave it on the drive a couple of weeks. When I tried starting it, nothing happened when I turned the key (no dash lights, no clicking, key fob not working) so I assumed the battery had died.
Got a jump start from a mechanic, who checked the alternator and said it was working great. I immediately drove to Halfords to get them to check the battery. They said it was in great condition.
Bongo started first time in Halfords car park and I drove home. All seems well.
It sat on the drive for a couple of days and when I checked it last night it is completely dead again.

I'm not sure what to try next. If the battery and alternator are both in good condition- why is the battery draining so quickly? I'm sure I'm not leaving anything on so is there something which could be draining it which I'm not aware of? Or maybe this second drain was due to the starter battery not having enough time to recharge on the trip to Halfords? I'm hoping I can see a specialist on Saturday ( assuming I can get a jump start) but any thoughts / advice is appreciated. Thanks!

[g8dhe]

You need in very rough terms / rule of thumb 20 minutes dual carraigeway driving to put back into the starter battery the energy you take out from a cold start. If its flat and two batteries then you will need several hours driving to recharge both.
However you may still have a parasitic drain, so use your meter to measure the current from the battery when everything is switched off, minimum would be 50mA and anything over 100mA needs understanding is likely to cause a problem.

[MalcW]

I had the same problem on my wife's car. I found the culprit by disconnecting the battery earth and putting a multimeter between the earth terminal and the earth cable, which then showed the current drain. It was then a case of pulling and replacing fuses one at a time until the offending circuit was found. Naturally it was almost the last fuse before I found it. It turned out to be the CD multichanger in that case, but as has been mentioned in this forum before, certain radios have a fair current drain even when everything is switched off.

Good luck!

[Flanners]

In the meantime buy and fit one of these, job done well for the short-term.

https://www.ebay.co.uk/itm/Heavy-Duty-B ... SwsE1aFZLJ