AGM battery for Gen 4/Gen 5 Prius/Prius Prime and observations on the 12-V charging system

No interestingly seems like this method of Toyota charging of 12V batteries is more than 20 years old.

I have a 2004 Toyota hybrid Alphard which I changed into a campervan over Covid lockdowns. After checking the Prius guess what is the resting voltage of the Alphard- you guessed it 12.2V. Well it got the charger treatment too. I have had 12V issues with the van. It has two AC units and driving very slow in hilly terrain with the AC going in hot weather had the battery voltage fall to 11.7V which trips faults and check lights. The inbuilt charger just cannot keep up with the load, so I have a volt meter in the van to check that.

I did a 500km round trip this weekend with the Prius, so will be interesting to see what the battery voltage is now. Checking the battery voltage will be added as one of the periodic routine checks e.g. oil level, tire pressure, coolant levels, etc. to do.

I must say I find it strange that the battery charging could be an issue. I had my gen3 Japanese 2011 Prius import for 10 years. It had 20 000kms on when I bought it with the OEM battery and I never had any battery problems and sold it at 120 000kms still with the OEM battery. It was the best car I had ever owned, absolutely no issues at all. Sold in a weak moment, but glad that I have another one now.

 

DO you know the voltages the Prius vehicle electrical system was subject to when you turned the "intelligent charger on and it went to the de-sulphating program" ?

 

No as I can't remember but some years ago I checked what it did and from memory it pulsed the battery at 14."something" volts.

14.7V pulsed
something like this
https://www.aliexpress.com/item/1005005389302164.html?spm=a2g0o.productlist.main.13.5f8042detgTbzy&algo_pvid=98e3cea6-29fb-46e9-84c7-2304f38be9d7&algo_exp_id=98e3cea6-29fb-46e9-84c7-2304f38be9d7-6&pdp_npi=4%40dis%21NZD%2125.98%2125.98%21%21%2115.32%2115.32%21%402101c5c317312844782771260efb9d%2112000032853324743%21sea%21NZ%21830455513%21X&curPageLogUid=4G6GrbsZCJ0e&utparam-url=scene%3Asearch%7Cquery_from%3A

 

Good to know that it does not apply a 15v or higher voltage in the mode you used. 15v or higher could cause problems with the cars electrical system and components.

 

Mine is a bit different to that one as it's only a 5 stage charger and only 6A . Mine does do the 15.5 or 15.7V charge (memory a bit hazy on exact what voltage it was) but you have to set it to the repair mode for it to do that. It doesn't go to repair mode automatically.

As you can see in that one's manual it always starts with this desulfation mode which seems like it sends a pulses and then measures the falling battery voltage
?? or pulse current? between the pulses to determine the state of your battery. After that it goes though the other stages. They work really well and have revived drained motorcycle batteries. I have one built in permanently into my Toyota hybrid Alphard running off the vehicle supplied 100AC to charge the house batteries.
I have had good service from these units for a few years now.

 

Yes I was pleasantly surprised that repair revived a motorcycle battery the was below 11V and I got about a year more out of it. I knew I was pushing it tho.

 

My 2020 Prime once again charged fully yesterday, and it wasn’t any 20 hours since the last time. It had been colder. Without the monitor it would be difficult to see the details.
I have yet to see it stop charging though in ready mode when it starts doing this. Of course the rate may be minuscule and it still is charging at 100%. Plus the Toyota battery sensor soc reading may be different.

 

I see about 14.3-14.4 v in ready mode in park. It seems to charge fast sometimes, other times slower. No amp scale to know. The 20 hour thing doesn’t seem to be a thing. SOC was around 80, distance was 3 miles, got home let it finish to 100% for about 12 mins in park appx. But it actually never stops charging, since no ammeter don’t know how low it goes.

 

Here's some data from the PP XSE with the original toy battery in service. Looks like it was at resting voltage about 12.38 v, the PP BMS charged it at just under 14.0 volts for a short time, then it rested at 12.70v for short time, then charge second time at 12.9- + for some time, then 12.79-12.61, then another READY state charging at for a moment at 13.90 then back down to about 12.78v charge, and then back up to 13.56.

I really do not remember the details of this data. Was just learning how to download it from the BM and send the file by email to my phone and laptop.

Just replaced the laptop with another of same make and a little faster and more storage space. Just got Microsoft 360 with excel working and started playing with insert graph function. Been years since I played with excel. Impressive program and features for making graphs of data.
Here's the graph I ended up with. It will be hard to view unless you do it with a bigger screen than an iPhone. Looks good on my laptop 16" screen:
(I see that the battery voltage black text itemized every 2 minutes kinda failed for legibility..
It was a blue text in the original image. I'll try and improve that appearance somewhat for future posts)

 

Also, rest voltage and SOC (state of charge) depends on the temperature of the battery:

This is for standard lead acid. There’s a similar chart for AGM batteries.

 

On mine there is up to five days of voltage history, I think the other common bm2 monitor goes to seven days. I put that kind on daughter’s Camry hybrid. What other graph is needed?

 

I have 4 BM devices in place on vehicles (AGM and Flood batteries) and one for Lithium batteries on a trailer with a LiFePO4 battery. Each one is a little variation of the voltage measured with a fluke meter. I think they all read a little low maybe by 0.1 volt compared to the fluke at 14v point. Its been a while since I compared the BM v to the fluke v, I'll check again when I have the opportunity and choose to spend some time doing that. I think you stated somewhere in one of your posts that your BM voltages do not exactly agree with meter voltage readings.