I think the battery on my Mk 4 Focus ST will need replacing soon. The cost Ford have quoted me is about 3x the price of a similar battery from Tayna (2x for the battery itself, then about another 1x for fitting). I have not been able to find photo or video guides of changing the battery on the Mk 4, so I'm not confident doing it myself.

My questions are:

1. If you have experience or know of any guides on changing the Mk 4 battery at home, can you share it? What tools are required?
2. Since the battery change involves messing with the BMS, would an independent local garage (not a Ford dealer) be able to do it?
3. If I replace the battery with a higher capacity one, like the Yuasa 096, would a BMS reset be enough, or would I need to additionally change the battery capacity using Forscan? Would you expect the garage to do it, or should I do it myself?

Thanks.

BMS reset can be done with a button/pedal combination.

BMS reset is enough, no need to mess with the car's config. (I only did because OCD).

The YBX7096 is what I fitted and got from Tayna. It's slightly taller than the Ford battery but the clamp still fits fine.

10mm socket I think undoes the terminals from memory, possibly the same for the clamp. I can't remember, as I had my whole socket set down there.

It's not that difficult really, although I did find I had to take the airbox out.

My car is a similar age to yours, my stop start doesn't work, so might need a battery in the near future, so would find a guide useful, I know it's not straight forward change the battery, not just tighten the positive and negative terminals, sadly.

The Airbox needs to be removed because the Battery needs to be slid forward to remove it after undoing the clamps, at least on the 1.5 Petrol,  otherwise it is not more difficult than other cars.

There must be something on YouTube that would give you an idea of what's involved. 

2 hours ago, Tizer said:

at least on the 1.5 Petrol,  otherwise it is not more difficult than other cars.

same on the 2.0 diesel, remove the airbox to make things easy. The whole job takes less than 30 minutes. All that is needed is a 10mm spanner or socket and a screwdriver to loosen the clamp on the airbox.

Thanks for your replies. So dealing with the airbox is as easy as pushing out some clamps and then pressing them back in? If so, I may have got intimidated for nothing...

Do you think it would be worth buying a battery charger and holding onto the original battery until it completely fails, or better replace it to be done with it? Right now I find that the SoC goes does from ~70% to ~55% if left for about 5 days, which seems like a big loss. But it didn't die completely over the holidays, so it's still holding some charge.

14 minutes ago, ansbenkq said:

Do you think it would be worth buying a battery charger 

I would suggest, if you haven't got one already, a "smart" battery charger would be a sensible investment given the number of threads on here regarding battery issues with Mk 4 Focuses and Mk 8 Fiestas. Many of us, particularly those doing low mileage, give our batteries a regular charge.

1 hour ago, Eric Bloodaxe said:

if you haven't got one already, a "smart" battery charger

then @StephenFord will be along soon with a picture and a link of a decent one for under £25 👍 🎉

 

3 minutes ago, unofix said:

then @StephenFord will be along soon with a picture and a link of a decent one for under £25 👍 🎉

 

Well, if you insist LOL Charger available from here...