My strategy for prolonging battery life (avoiding full charge)

I have developed a system that I think works well for charging my 2026 Prius PEHV.

My strategy is to charge as late a possible and avoid fully charging to preserve the battery heath. (Yes I know about the 15% built-in headroom, but more is better.) My system is simple: I have set up 9 different charging schedules which range from charging for 2 hours to charging for 10 hours in 1-hour increments, and power rates are 1/2 price from 7pm to 7am, so each of my charging schedules ends at 7am. And for my car, each hour of charging adds 10% of battery capacity (regular 110V, 15A plug).

When I plug in for the evening my routine is to select the schedule which will bring the battery to between 80-90% charge. So take 10's digit of the battery percentage, subtract 1, and enable the charging schedule that starts at the time. For example, if the battery is at 35%, I enable the schedule that starts at 2am. The car will then charge for 5 hours, from 2am to 7am, adding about 50% charge (a bit less in cold weather), and bringing the battery up to about 85% charge.

I usually don't bother charging if the battery is already over 70%. This handles my about-town driving needs for most days, but if I know I'll be driving more or less the next day I'll adjust the charging time as necessary, sometimes bringing the car up to 100% charge, and other times not charging at all. An important point is to always end the charging as late as possible (7am in my case to take advantage of the cheap power), so the battery is at the maximum charge for the minimum time. Also, charging during the coolest time of day like this will have the additional benefit of avoiding overheating the battery when the weather warms up.

- Phil