FoxESS Community - Owners & Installers Forum

All posts I've found about hot water systems and batteries are on how to connect it, not disconnect it, so sorry if I missed a post about this topic.

Our situation is we just got a new battery system installed and the battery is discharging when it notices the hot water system has started drawing current. This will just wear out the battery faster than it needs to be.

In 2 weeks time after the change of plan cooling off period we're going to get 3 hours of free power a day and I want both the hot water system and the battery to use power from the grid at the same time. Currently the battery limits the current from the grid to about 6kW but the hot water uses 3.6kW.

The meter box has a timer for the hot water and I tried shifting the house clamp from the mains lead to the 4 circuits that need monitoring but that sent the battery a little crazy regardless of direction I turned the clamp.

Does anyone have any advice about where to from here?

The hot water heater will be normal house load and so the inverter will see it and try and supply it as you say - is the hot water being heated on a low tariff?, what most people would do is to set a force charge with a low power so that the battery doesn’t get used (but charges slowly instead).

Dave Foster wrote: ↑Sat Feb 14, 2026 6:26 pm is the hot water being heated on a low tariff?

There is 3 ToU periods on our current plan. Shoulder and off peak are charged at AU$0.32/kWhr. Peak is AU$0.57/kWhr from 5pm to 8pm week days. The daily connection fee (tax) is AU$1.98/day.

Once the new plan comes into effect there is still 3 ToU periods. Off Peak is free between 11am and 2pm because there is way too much roof top solar hitting the grid then and the price to export to the grid goes negative and that's how our power company can offer it for free and still profit.

Peak will be AU$0.52 from 4pm to 10pm, and shoulder will be AU$0.39 the rest of the time. The daily connection fee (tax) will be AU$2.07/day but if we don't use more than 30Whr per hour from the grid between 6pm and 8pm we pay $1/day less.

So it will be less than AU$1.20 per day going forward as the battery isn't wired to prevent grid use outside of the free period, well not yet anyway.

I can't remember the last time we would have had a power bill that low, especially when the prices almost doubled during COVID due to inflation coming out of lock downs.

Dave Foster wrote: ↑Sat Feb 14, 2026 6:26 pm The hot water heater will be normal house load and so the inverter will see it and try and supply it as you say - is the hot water being heated on a low tariff?, what most people would do is to set a force charge with a low power so that the battery doesn’t get used (but charges slowly instead).

Testing since installation shows the battery can continually charge at 4.8kW. Over 3 hours that works out to be more 14kWhrs which is about all we use a day (not counting the hot water) and we have 4kW of solar panels which don't do very much on cloudy rainy days in the middle of winter, so just having the battery alone will work very well for us.

Testing last night when the hot water was drawing from the grid I set the schedule mode to backup rather than forced charging. The battery floated after hitting 80% and didn't discharge for the hot water system or anything else in the house while floating.

While that's not great on our current plan, it will be perfect for the new plan. Solar exports to the grid is only AU$0.03/kWhr, so as much self consumption in next 2 weeks will help, but it's been very overcast and rainy since the battery was installed. Buying non-peak power is saving us about AU$1/day.