# A little lithium backup power **URL:** \ **Category:** General\ **Created:** [October 2, 2026, 4:39am UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601 "2026-10-02T04:39:32Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![PaulM](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/paulm/32/59_2.png) [@PaulM](https://nonsuch.discourse.group/u/PaulM)\ **Post date:** [October 2, 2026, 4:39am UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/1 "2026-10-02T04:39:32Z")
I just added a 100Ah LiFePO4 battery to my existing AGM house bank for a little rainy day “range extension”. It’s a pretty simple concept. I use less power than my solar can generate on sunny days so why not save it? I’ll let the pictures explain but basically I installed two DPDT switches (only one actually needed to be DPDT) to switch the solar input and battery output to my panel from AGM to LFP. Both are On Off On configuration to keep the banks totally isolated and to make sure the solar array is disconnected while the batteries are switched. The switches I bought were not as intuitive as my sketch so I asked AI to give me the pin out to save me a bunch of testing. It was perfect the first time. I just got it up and running yesterday and now I’m looking forward to seeing it do its stuff. This album should explain better. [![Google Photos](https://canada1.discourse-cdn.com/flex011/uploads/n26_115_233/original/2X/0/02ebbf1f5f9e2988c8912eeef7babb598aab30c5.jpeg "DCHouse LFP Backup · Sep 22 – Oct 1 📸") ](https://photos.google.com/share/AF1QipOUkfhJcrSfK16s78-3cpWn16Dd60eie5ePtPOroK67jgu6tEWN5K7RoaH8MTvELQ?key=ZUVQdzM5dWZUZmxiTmhSaGN2aG11RTVRbkJwanR3) ---
**Author:** ![thorpowell](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/thorpowell/32/799_2.png) [@thorpowell](https://nonsuch.discourse.group/u/thorpowell)\ **Post date:** [October 3, 2026, 3:48pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/2 "2026-10-03T15:48:39Z")
AGM and LIpo use very differenr chargng profiles for a reason. One battery will either be under or over charged and that can be dangerous. What is happening on the dischaghe side ? You defrinately can not have the two batteries in a combined state. I would resist the urge to use AI for wiring adivce. I have asked AI a few questions regarding an electical issue I am working on and it was far from accurate. ---
**Author:** ![PaulM](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/paulm/32/59_2.png) [@PaulM](https://nonsuch.discourse.group/u/PaulM)\ **Post date:** [October 3, 2026, 6:07pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/3 "2026-10-03T18:07:41Z")
I’m running the controller on AGM profile. When switched to LFP it will as you say not fully reach 100% but that is fine with me. The switches are both on-off-on configuration so there is complete disconnection between the batteries and the array is shut down as the batteries are switched. As for AI, I’m happy to use it where I can verify its recommendations. In this case it was easy to check and AI had it right, saving me time figuring out the terminals. ---
**Author:** ![thorpowell](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/thorpowell/32/799_2.png) [@thorpowell](https://nonsuch.discourse.group/u/thorpowell)\ **Post date:** [October 3, 2026, 7:13pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/4 "2026-10-03T19:13:58Z")
Does not work like that . Li does not “like” the bulk voltage , absorbtion stage and float that AGM settings have. Cell wll never balance . Cells out of balance will destroy the bank and the BMS may throw in the towel . Conversely using Lipo setting for AGM will not have the absorbtion and float that AGM’s require, you will boil the battery. Using AGM settings will prevent Lipo cell balancing, cause the BMS to disconnect and none of this is good. It’s not getting to 100%. that it is how the cells are treated that matters. You can get any acid battery to 100% @ 15 volts as well, but the battery will last only a few charges. You might get away with it for a while. ---
**Author:** ![PaulM](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/paulm/32/59_2.png) [@PaulM](https://nonsuch.discourse.group/u/PaulM)\ **Post date:** [October 3, 2026, 7:23pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/5 "2026-10-03T19:23:47Z")
You got me Thor. I listened to AI once too often. It does lie outright to you sometimes. It was dead right about the switch positions but it spun me a real beauty about the charging profiles. It actually told me that because it wouldn’t hold the high V on the battery (lfp) when full AGM profile was “the perfect compromise” for my setup. My bad for not checking elsewhere. However, not to throw the baby out with the bathwater as it were, I can still manually change profiles when I change banks. Thanks for catching me. 😅 ---
**Author:** ![NS233\_Bob\_Neches](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/ns233_bob_neches/32/120_2.png) [@NS233\_Bob\_Neches](https://nonsuch.discourse.group/u/NS233_Bob_Neches)\ **Post date:** [October 3, 2026, 7:24pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/6 "2026-10-03T19:24:08Z")
> [@PaulM](#): > > As for AI, I’m happy to use it where I can verify its recommendations. My AI credentials are a bit out of date. They start with having received a 1976 Bachelor’s Degree for Independent Studies in Artificial Intelligence. They mostly end in 2013, when I retired as the director of an office in the U.S. Intelligence Community that funded many of the precursors of the work you’re seeing marketed today. (Plus a few articles since and assistance provided to a colleague on a book about to come out.) I feel strongly that Paul’s approach is the right way to use what’s being marketed as “AI.” It’s important to understand that what’s being marketed as isn’t really “intelligent”. It uses sophisticated statistical analysis of enormous amounts of data that has to be very specially pre-processed. This enables “AI” to handle a large range of requests. What it does with them is generate outputs that are _likely_ to be plausible because they are statistically _similar_ to what the sources of the original data might produce. This makes its quality very sensitive to the expertise of those who prepared it. And also very sensitive to exactly how you pose questions to it. The preceding paragraph is just a fancy way of saying “If garbage goes in, garbage comes out.” “AI” is truly a “Trust but verify,” technology. It’s improving. But its only as good as the material that it’s trained on. Its skills at looking and sounding plausible are improving faster than its accuracy. _Seeming plausible_ is easy – lots of people are good at, and therefore produce data that can be used to imitate them. Being _right_ is harder – that depends on very careful expert oversight. It does seem almost human. And, in a sense it is: humans are fallible. Sorry for the long rant, but 50 years of connection to the topic generates strong feelings. A lot of important considerations have been thrown under the bus in the rush to market. Again, not a diatribe against using “AI”. Just trying to explain the case for using it the way Paul did. If it’s saving you time on a task where you know enough to check its work, great. If not, be very careful with depending on it. -- Bob ---
**Author:** ![thorpowell](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/thorpowell/32/799_2.png) [@thorpowell](https://nonsuch.discourse.group/u/thorpowell)\ **Post date:** [October 3, 2026, 7:30pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/7 "2026-10-03T19:30:05Z")
So Bob you are saying it’s like listening to my mother in law…… ---
**Author:** ![NS233\_Bob\_Neches](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/ns233_bob_neches/32/120_2.png) [@NS233\_Bob\_Neches](https://nonsuch.discourse.group/u/NS233_Bob_Neches)\ **Post date:** [October 3, 2026, 10:21pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/8 "2026-10-03T22:21:56Z")
I’m waaay too cautious to be quoted saying _that_. It’s more like putting your faith in a YouTube video that’s gotten a bunch of likes. Ya win some and ya lose some. Whether using AI or YouTube, I’d suggest there are some definite benefits to getting second opinions from the INA Community Discourse Forum. -- Bob ---
**Author:** ![PaulM](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/paulm/32/59_2.png) [@PaulM](https://nonsuch.discourse.group/u/PaulM)\ **Post date:** [October 3, 2026, 11:00pm UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/9 "2026-10-03T23:00:36Z")
Soooo… I confronted my old buddy Al about his interesting interpretation of truth… and he (it, but I like he) waffled a bit and then said that it actually was possible but not with default profiles. He then offered a “user defined” custom profile that he claims will solve all my problems and will program on my controller. I stated my reservations and asked for a clean description that I could run past a human expert. The following was his suggested profile. It looks totally logical but as Bob says, he is getting very good at looking plausible… ![Screenshot_20261003-160624](https://canada1.discourse-cdn.com/flex011/uploads/n26_115_233/original/2X/0/094ade2f3a57314b0ad5e3599b871fae4691553f.png) ![Screenshot_20261003-154908](https://canada1.discourse-cdn.com/flex011/uploads/n26_115_233/original/2X/a/a26d311ed1444842e6740f4919811dffba39bf2f.png) Would anyone like to be the expert? ---
**Author:** ![thorpowell](https://yyz1.discourse-cdn.com/flex011/user_avatar/nonsuch.discourse.group/thorpowell/32/799_2.png) [@thorpowell](https://nonsuch.discourse.group/u/thorpowell)\ **Post date:** [October 4, 2026, 1:21am UTC](https://nonsuch.discourse.group/t/a-little-lithium-backup-power/10601/10 "2026-10-04T01:21:22Z")
So I got a rather rude suprise. Generally I make sure my batteries are fully charged particlaul over the winter. OPS, LiPo should be stored at between 40 and 50%. So now on a boat that mever uses more than 18 amps a day I need to figure out how to drain 150 amps….. is there are drain tap on these things….