3394Prius NiMH Batteries
- Dec 24, 2007Hello Bill
I am not an expert on the Prius NiMH packs. I have though done quite a bit
of research on NiMH batteries and have been using them for several years now.
What Mike has pointed out to you about the Prius being optimized for
accepting regen is true. I have read information from different NiMH battery
manufacturers web sites. It is used as a sales tool to sell their batteries for
Hybrid vehicles. The Prius pack is never fully charged and never deeply
discharged. I recall it is 50 to 80 percent SOC they are maintained within.
Heat is a real killer of all NiMH batteries regardless of the battery mix or
use. In the Ranger and RAV4 they will stop charging if the batteries are not
cool enough. The S-10 and EV1 use A/C to keep the NiMH batteries from
exceeding 86 degrees during charging. It is the last 20 percent of a full charge
that NiMH batteries temperature really takes off. As I see it the Prius
batteries were never to go the last 20 percent of a full charge. The packs were
never intended to have to deal with this much heat.
Also the NiMH battery does heat up under large current draws. They also heat
up even more during hard draws in a lower discharged state. This is not
because the Prius pack was never to deliver the power for full EV use. The more
power you pull from them the more they will heat up. You could very well kill
these batteries during both charging and discharging this would destroy them
The used Prius packs may be a real buy however I doubt they would provide
long life if used as an EV battery. Unless you really oversized the pack and
kept them within their design temperature range and power draw. I am certain
the results would be very disappointing.
It would be interesting to know more about Mikes testing.
1998 S-10 NiMH
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