I’ve checked voltage using voltage section on my icarsoft OBD reader, and I’m getting 2 different readings. If it’s been sitting overnight or for a while it’s reading 11.8V but if I test immediately after driving it’s around 12.2-12.4V. If I leave it half hour it’s back to 11.8. Is there a charge held in batteries for a short while after turning off?
Ive had a battery test at a auto shop and it’s tested good but that’s straight after car is turned off. It’s a 2001 Volvo V70 XC

 

What does it read while car is running? Sure sounds like you have a bad cell in the battery to me since you have no voltage change from half hour to overnight. That rules out parasitic draw.

 

Are you having a problem with the car starting? Or you just want an explanation for the 11.8 volts? How old is the battery?

If the car starts ok - leave it alone. If it does not, replace the battery. Or if you are worried about the 11.8 volts - replace the battery.

 

Whilst it’s running it’s around 13.5-14 which is good. Stop it and it’s around the 12s but after 10 minutes or so it drops to 11.8. 11.8 is low / bad. No issues starting yet but about to head into winter and have had the odd sensor communication error thrown which I know in some cases can be a low battery.
when I got a battery test done it’s ok but that’s because I’ve only stopped the car. That’s why I’m asking if there is a surface charge of sort so should battery test be done after the 10 minutes?

 

Assuming Australia.
If so I may find the need to mock you about your winter comment.

How old is the battery? High heat areas can do bad things to batteries more so than cold sub freezing areas.
How was the battery tested? An electronic tester or old school carbon pile one? Carbon pile ones are much better at testing and showing issues with marginal batteries.
After sitting over night is the voltage still the 11.8V?

 

it’s still 11.8 overnight so no battery drain. I’m now assuming these cars have a surface charge which lasts a few minutes. Battery test was electronic at the auto store. And at home it’s me using the voltage on the OBD reader.