Add option to prioritize reserve capacity (hold float mode indefinitely)

[menningd]

In some installations such as mobile applications there is a preference towards maintaining a fully (or mostly fully) charged battery, and expecting charge sources to offset any parasitic loads while in this state. Installations like these can have the battery sitting for extended periods (weeks or even months) of time whilst expected to maintain preparedness for a full discharge cycle. Presently the DIYBMS firmware is tailored more to ESS's where daily charge/discharge cycles are expected. The result of using the current firmware in an application such as, e.g. a boat thats kept plugged in to shore power, is that the parasitic loads will continously short cycle the battery between 100% and 95% (or whatever the SOC resume charge is set to) every couple of days.

As a further enhancement to "charge modes" there should be an option to disable the float timers expiration so that it stays in float mode indefinitely. Then the battery can be kept at a high SOC and the charger will handle supplying parasitic loads without trying to force anymore charge into the cells. Of course it is vitaly important to set the correct float voltage for the cell chemistry. And the battery will have dropped down to 95-98% SOC once it reaches this float voltage. But this is the best compromise for these types of applications.

I will begin looking into this proposed enhancement but was curious of any other feedback.