Sell ep5 for ep12? Or stick another ep5 in?

[carrot1401]

Hello! I need some feedback on whether it's worth replacing my EP5 with an EP12. We got the system installed in April 2025 and it's been brilliant. The ep5 is non heating version that has done 572 cycles, with a SOH of 92%. In hindsight I should have went for the ep11 but I didn't know at the time that you cannot mix and match different sized batteries. With recent weather we've drained the battery overnight with fans, and regularly drain it quickly in the winter months as I usually game on my PC in the evening. So I have 2 options:

• Grab another ep5 with a junction box, and have no heating element. I think I read somewhere about mixing different SOH not being a good idea, but someone please correct me.

• Grab an ep12 with heating element and try and sell my ep5 (no idea what it would go for....or even if I could sell it?!?!)

What do you lot think? I have a H1 Gen 2 inverter and 5kw/h export, with 12 panels (but I doubt that changes anything here)

[MaterialBarracuda48]

What energy tariff are you on? Is it same rate 24/7 or do you have cheaper night time prices (EV / heat pump / E7 etc?)

Do you have plans in the future to have a heat pump for example in next few years?

[carrot1401]

What energy tariff are you on? Is it same rate 24/7 or do you have cheaper night time prices (EV / heat pump / E7 etc?)

Do you have plans in the future to have a heat pump for example in next few years?

Octopus agile, so we try our best to shift load. Am aware the last few weeks have been not as good as previous months but our bill for July showed us importing just 36.7kWh at an average price of 4.36p/kWh costing £20.97, while we exported 602.9kwH and made £72.35 (we were on holiday last week of July). So far in august it's 21.1kWh import and 247.38kWh export.

No plans on heat pump or electric car in short term; very well believe in "if it ain't broken, don't fix it" and boiler is fine. Car may change in 2028 but would look at getting vehicle to load charger and have a 50kw+ battery on wheels

[MaterialBarracuda48]

I am on Agile too, have an EP11 to mop up the cheaper electric times.

From your figures, it doesn't seem like you use much electric, which makes me think it might not be worth it?
Do you have 'To load & battery' & 'From PV & Battery for July (aware the holiday will skew it) Ideally, can you take 3 weeks and add those figures up, and then divide by 21 days to get your average daily?

So let's say you are using 8kWh each day, then you might only be buying a little amount in, so you don't need EP12 levels of storage. I am aware Winter will change the amount of import of course.