NiMH or Lithium?

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Joined: 31/12/2012
Location: New Zealand
Posts: 9192
Posted: 02:06am 22 Mar 2023      

Thank you for all the replies.

...and welcome aboard, Andy.

The units only draw power when they transmit, and that is only sporadically.  Many of them can go MONTHS without a single transmit cycle, as they are only used when needed.

This is what has got me thinking about using Lithium batteries as a backup rather then the NiMH I use now.  The long-life Lithium batteries are now CHEAPER by almost six bucks per battery, then the rechargeable NiMH type.

Mains power is very reliable.  Sometimes there is an outage, but it only lasts for a few hours at most - they're pretty good at getting the juice back on again if it fails.  Not counting planned outages, the power can be reliably on all year round, so the battery only needs to catch the occasional power failure.

The units monitor the battery voltage, and can send a low-battery alert now, so I would naturally keep that in place, but remove the trickle charging resistor from the design.  Or maybe leave it there, but connect via a couple of solder-blob pads, then you can use either type.

Wouldn't be talking about this a few years ago, cos Lithium batteries were still so bloody expensive(for quality ones), but they have come down a lot in price over the years, and are at a point now, where they are CHEAPER then the rechargeable type, but they have the advantage of possibly outlasting a NiMH on trickle-charge over a long period of time.

Yes, when they are flat, you have to replace them, but after ten years or so of constant trickle, most NiMH batteries also need replacing cos they won't hold a charge anymore, so this is what set me off thinking about switching.  That, and I also have just recently changed the designs to use RP2040 modules due to lack of PIC32 chips, so I'm already making changes - why not the battery concept also? (rhetorical)

  Mixtel90 said  I would say that, if the mains supply is pretty reliable and only short disruptions are likely then non-rechargeable lithium is the way to go - but recycle them. You should get somewhere around 8-10 years life before they need to be changed.

That's kinda what I was also thinking and I think is how I will now proceed, but I wanted to post a thread, to see if it was just me thinking that.  

Thanks to all.