UKH

Supplies running a bit low, so went to do a shop earlier, and my battery in the car is dead (8.2V). Managed to rig a powersupply to it and left charging for 3hours, no change in voltage.  The indicator disc on the battery is black, so I think I need a new one....

Fortunately Halfords will deliver me one saturday if I order today.... couple of Q's... will the new battery arrive charged enough to start the car so it's just a matter of swapping the battery out?

I realise I may have an issue with alternator, but figured the battery is the most likely suspect as the car has been sat still for 5 days (and I left the dashcam plugged in)

Yes it'll be fully charged. If you've got a newer car make sure you have the codes to anything that needs it.

You can do a rudimentary test of the alternator with your multimeter to see what volate and current is coming out from it. Although as we discovered recently with my girlfriends car they can still be faulty but appear to be working ok.

Probably.   Be kind to it those and give it a charge if you can.

The famous "just" - if you have a chance in advance, put a bit of penetrating oil onto the nut/bolt holding the battery strap/clamp in place, and onto the height adjusting bolt (if there is one) on the other side of the strap/clamp, incase the replacement one isn't exactly the same shape/size.

You can always try a "desulfator" on the old battery - some maintenance chargers include this.  

Now is a good time to get a maintenance charger and occasionally hook it up to your car if you can; doing occasional short trips to a local shop isn't kind to the battery.

Unless you habitually ignore warning lights on your dashboard there was probably a persistent red battery warning the last time you drove, if this was the case.

Cheers,  battery lights etc all normal last time it ran, and I've got a charger i can top it up with before starting so will do that as much as I can and got a trickle charger arriving next week to rig it up permanently

Should be 14 volts with the engine running if the alternator is working properly. Sounds like it is though if no warning lights have lit up.

What voltage did you try to charge it with?

Be very careful swapping out the battery, my son's Peugeot was fooked after changing the battery as if knacked up the EMU and we couldn't sort it out.

ps. I don't know how you change the battery without EMU issues,

I say this as a once proud owner of a 306

Don’t buy a Peugeot?

charge won't necessarily change the voltage, but at 8v the battery is proper gone. cars usually struggle to start at 10v. if it's >10yr old it's probably just died of old age.

as others have said:

new battery will be charged, and have power enough to start engine.

check your instruction manual for codes etc. interrupting power to the systems can cause stuff to reset, or worse, lock up.

14v measured with engine running - alternator is prob fine.

changes 2 in the past year; and couldn't be bothered with the jiggerypokery of maintaining power connection while changing. didn't have any bother except, reset clock and radio.

Look at the power of the current battery eg 50Ah. You may be able to get one with a larger charge capacity e.g 70Ah, with the same physical dimensions, for not much more. This will give you more grunt starting on those cold winter mornings (yes, I know we're going into summer) and it will also hold a charge longer, if you do have an electrical fault.

Some modern cars won't start if the voltage is below 11.5 thanks to the inbuilt CANBUS ECU logic. Bit frustrating where older cars would chug and catch, the newer ones don't even try.