Video Tutorial How to deep discharge your NiMH Battery pack instead of replacing it (Insight/Civic/Prius)

[Cash68]

Hey Guys,

Haven't posted here in a while! My daily is still a 2000 Insight, and I bought it with 180k and a non working IMA system. I installed a grid charger and that limped me a long for a few years, except it worked for a shorter and shorter time period before charging. I was pricing out getting a replacement pack ($2000ish), and that's when I started reading about the success people were having with deep discharging their packs. Since my pack was sort of messed up anyway, I figured why not try this first before replacing it.

I read a TON of threads about this process, and tried it. It made a HUGE difference in the usability of my pack, and instead of grid charging 1x a month, I was able to go 2-4 months or more between grid charging. This lasted over a year, and I did it again. I've done it four times over the past 4-5 years and I'm always amazed at what a huge difference it makes, so this last time I documented my process on youtube. Please check it out and give me any feedback or ask any questions you have.

Before you replace your pack, at least TRY this, you have nothing to lose and thousands of dollars to gain.

https://www.youtube.com/watch?v=V9dUnq8NxUs

Feel free to sub if you want, I don't put out a ton of hybrid content, but I do try to make maintenance vids for the insight when I can.

[S Keith]

Grid charging exacerbates voltage depression while improving cell balance. Voltage depression is the phenomenon that results in lost capacity.

In other words, the act of grid charging necessitates periodic discharging to ensure capacity is not lost.

In most cases the vast majority of benefit of discharging is obtained when discharging to 0.8V/cell or about 96V for an Insight/HCH1. Deep discharges can readily push a pack with a marginal cell into failure.

In the vast majority of cases, if dramatic improvements aren't had by 2X discharges to 96V, there are no dramatic improvements to be had. Only after 2X deep discharges to 96V haven't paid off should an ultra-deep discharge to the depths near 0.1V cell be attempted - mostly as a Hail Mary before you replace a dead pack.

[Cash68]

The hail mary definitely worked with my pack. Are you saying that now that it's working, I should only go down to 96V until 96 doesn't work anymore?

[S Keith]

Originally Posted by Cash68

The hail mary definitely worked with my pack. Are you saying that now that it's working, I should only go down to 96V until 96 doesn't work anymore?

The Hail Mary probably wasn't needed vs. 2X discharges to 96V, but it worked.

Grid charging should be done as needed to maintain cell balance.

Discharging should be done only as often as needed to maintain performance.

A single discharge to 96V 1-2 times per year should suffice.

[Cash68]

I'll try only going to 96v next time... but what do you mean by 96v?

As soon as you remove the load, the voltage springs back up.

[S Keith]

Originally Posted by Cash68

I'll try only going to 96v next time... but what do you mean by 96v?

As soon as you remove the load, the voltage springs back up.

That's how electricity and batteries work.

"discharge to 96V" is literal. Discharge to 96V and then stop. Voltage not under discharge doesn't matter.

Trying to discharge repeatedly to make a NiMH battery STAY under any given voltage is usually a recipe for failure.

A cell completely empty of any usable charge will rest at about 1.2V. Thus a 120 cell pack that has had 100% of its usable capacity removed will still seek about 144V.

[Cash68]

Whatever, it's still working fine so I am doing something right.

[S Keith]

Originally Posted by Cash68

Whatever, it's still working fine so I am doing something right.

LOL... 3 months later.

No. You're not doing something right. You're doing something that works for you. You have a healthy battery with strong cells, and they are tolerant of the abuse. Many have marginal cells and will not respond well to this treatment. On several occasions documented on IC, it has taken a pack that can continue to limp along with grid charging and forces it into full cell failure and permanent P1449.

Part of developing expertise is considering more than just your experience and not assuming that everything will work for everyone the way it works for you. Not a reasonable position on 14-20 year old batteries. People with extensive experience have seen the consequences of unmanaged/aggressive deep discharges and don't do them anymore.

[Cash68]

Still working. No IMA light. Works awesome. My pack is not strong or healthy, and didn't even work when I purchased this car 7 years ago.

[Cash68]

Still working, no IMA light. Honestly haven't even done a grid charge since my deep discharge this summer. Maybe I did one, but that was 3+ months ago, I don't remember.

DEEP DISCHARGE GANG 4 LYFE!!!