This. Lidl/Aldi have had them in recently for £14
FWIW if you go back to where they replaced the battery they will be able to run a check on it.
It should show the rating of the battery and what it's currently running at.
If it's weak they can tell and you can decide if you want to replace it so you're not stuck.
Jumping modern ECUs isn't great for them according to my friendly local mechanic.
Our Mini had it's original battery replaced in January - 14 years after it rolled off the line.
Last week the replacement with a 3 yr guaranty failed completely.I jumped it and took it to have the brakes changed (prebooked) asked my mechanic to check the battery but not to replace it.
Dead as a dodo, wouldn't accept a charge as it had an internal fault.
I took it back to where the battery was fitted and while they grudgingly agreed it was faulty they kept coming up with lines about "only 2000 miles since January", "it's not been used properly", "You need a trickle charger mate".
I pointed out the car usage hadn't changed - a couple of 20-40 min runs a week the odd longer trip - and the old battery had lasted 14 years - their reply "They don't make them like they used to though do they?" //static.avforums.com/styles/avf/smilies/facepalm.gif
I was tempted to say "So you're selling junk then?" but bit my tongue.
It has another 2 yrs guaranty - I'll keep getting it checked when the mechanic works on the car and getting it replaced if it dies.
Next time - if there is one - I won't be using a Platinum brand battery even if the car is dead on a cold January evening and they're the only place open!
Never had a problem charging a battery with the leads connected, but ideally you should charge the battery in a well ventilated area and avoid sparks in order to avoid explosive gasses being ignited. You can cause all sorts of problems by actually disconnecting the battery...personally if I was disconnecting a battery I would always keep the car's electrical system energised by connecting the battery leads to a second 12 volt source, either a second battery or a low voltage source plugged into a 12 volt socket in the car.