Good evening, I’m a newbie to the forum and not very (electrically) tech savvy.
A bit of bio first, I had a pv installation in July this year with a Fox EP12 battery and 12 Sunpower 510w pv panels. In July I also bit the bullet and had anASHP system installed.
Having had such a good summer, to date I’ve only spent about £5 on electrical energy usage and I’m on a low standing charge tariff with Octopus. As winter draws on with lower solar charging and the heat pump coming more into use I’m looking at changing my tariff.
In comparing tariffs, how long does it take to force charge the battery from 10% to 100%?
Thanks, David
There are a number of variables that will effect the charge time, the most significant is the size of the inverter as that capacity will be the maximum charge rate of the batteries - what inverter do you have H1-x, KHx ?
The good news is the EP12 battery has a high voltage and also a battery warming function (which you should use) as that will also be a major factor on charge speed in the winter months (everything below 16C begins to be throttled).
The good news is the EP12 battery has a high voltage and also a battery warming function (which you should use) as that will also be a major factor on charge speed in the winter months (everything below 16C begins to be throttled).
I find with my KH7 and EP11 that the temperature throttling occurs below 22°C, and the rate changes below that in stages.
So above 21.9°C is full rate.
Octopus Cosy is what you will need to swap to for Winter, 8hrs of charging.
As Dave has said, there is a heating function available (firmware levels permitting) for your battery. Depending on where it is stored, inside or outside the house, you can insulate it and then you won't need as much heating.
Mine is in a garage, and I basically chucked a small blanket over it, taking care not to cover the wires up.
So above 21.9°C is full rate.
Octopus Cosy is what you will need to swap to for Winter, 8hrs of charging.
As Dave has said, there is a heating function available (firmware levels permitting) for your battery. Depending on where it is stored, inside or outside the house, you can insulate it and then you won't need as much heating.
Mine is in a garage, and I basically chucked a small blanket over it, taking care not to cover the wires up.
Forgot to answer it more directly for you, with my previously mentioned equipment.TR2implant wrote: ↑Mon Sep 21, 2026 9:33 pm In comparing tariffs, how long does it take to force charge the battery from 10% to 100%?
Under perfect temperatures, ~1.5hrs. You have a little less inverter power, and a bit more energy to store, so expect to budget nearer to 2hrs.
The time to charge will increase when colder, it's important to insulate the battery where possible, and to use the heater function as backup... because if you enable heating, the battery doesn't charge at the same time (unless they have fixed this) Good news is charging does heat the battery up a fair bit, so although the rate might start off slow, it will increase.
Thanks @MB, Fox have been quoting the 16C and so I wondered whether the latest firmware had reduced the throttling from the 21C down to 16C, but certainly agree all models of battery in the UK ‘used’ to begin throttling as it falls past 21C. The good news with the EP12 nominal voltage at 384V it means you can lose quite a bit in throttling before you would notice it drop below the ~6kW max charge rate.MaterialBarracuda48 wrote: ↑Tue Sep 22, 2026 8:50 am I find with my KH7 and EP11 that the temperature throttling occurs below 22°C, and the rate changes below that in stages.
So above 21.9°C is full rate.
Anyhow, with a 6kW H1 you should be fully charged from 10%->100% in less than 2 hours under most conditions.
With a heat pump, totally agreeMaterialBarracuda48 wrote: ↑Tue Sep 22, 2026 8:50 am Octopus Cosy is what you will need to swap to for Winter, 8hrs of charging.
I am still running the older v1.011 FW, so the temperature points could be changed for sure.Dave Foster wrote: ↑Tue Sep 22, 2026 10:16 am Thanks @MB, Fox have been quoting the 16C and so I wondered whether the latest firmware had reduced the throttling from the 21C down to 16C, but certainly agree all models of battery in the UK ‘used’ to begin throttling as it falls past 21C.
Maybe I need to get that battery FW loaded on, if the full rate kicks in ~16°C
Would be nice to see some proper firmware release notes... come on Fox!
Thanks for all your replies. I was considering Cosy as my option anyway so at least that confirms that idea. My battery is outside, although I have just boxed it in, albeit hit and miss cladding so boxing still ventilated
IIRC you need a battery FW of greater than v1.009 for heater controls to work.
So, it's worth checking what firmware version is on your battery, and also checking in 'Quick Settings' that your 'Battery warmup' option exists, and can be enabled. Unless this has been fixed, you cannot warm the battery and charge at the same time, so if you do need to use heater controls, you are best using them on the longer (3hr) cosy cheap periods for the first 30-59 mins (04:00 to 04:29 / 04:59 for example)
Insulation is going to be your best overall choice vs. heating, with the simple blanket, I no longer needed any battery heating in the garage, outside, it will help keep warmth in (or some posh kingspan!)
So, it's worth checking what firmware version is on your battery, and also checking in 'Quick Settings' that your 'Battery warmup' option exists, and can be enabled. Unless this has been fixed, you cannot warm the battery and charge at the same time, so if you do need to use heater controls, you are best using them on the longer (3hr) cosy cheap periods for the first 30-59 mins (04:00 to 04:29 / 04:59 for example)
Insulation is going to be your best overall choice vs. heating, with the simple blanket, I no longer needed any battery heating in the garage, outside, it will help keep warmth in (or some posh kingspan!)