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To start off, I am aware that neither battery type should be “trickle charged”.

That being said, I have a product that really needs to randomly “trickle” charge a rechargeable battery. I have a device that will have sporadic and unreliable solar energy as the only source. While the device is low energy, it also contains some power hungry sensors that need to turn on once a day or once a week. The power required is above a reasonably priced super cap (would need ~500F at least). So my solution is to use some NiMH AAA batteries or a Lithium Cell. The reason I believe trickle charging could be ok is because I do not need anywhere close to the full capacity of the battery, so I would set a max charge voltage to below the nominal full cell voltage, and use a current control charge to limit it to a safe charge current, so the cell is charged in a safe manner until it reaches some voltage below the full cell voltage. I.e. for a NiMH that has a full cell voltage of ~1.5 I would charge to 1.35V.

I’m unable to find any information on this type of setup online, it seems all the typical trickle charge questions are about trickle charging to full capacity and beyond, which is a no-no for both the named chemistry above.

I’m also aware this is not an ideal situation and testing would need to be done to ensure the batteries hold up alright in this configuration. If anyone has any advice for alternative storage systems I’d be thrilled. I’m limited to ~1/4W of solar power and the device needs to operate for a few minutes at a time with a peak power of ~1-2W.

Edit:

So after reading some posts on Stack Exchange, and the comments below, it seems like partial charging of Li-ion is a good solution since at most I only need 50% capacity. The internet is full of stories about how dangerous Li-ion can be that I have mostly avoided it, but in this case, it seems to be a good solution other then the wide temperature range that I need to look into.

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  • \$\begingroup\$ I see another post with similar information just was posted, so it sounds like this may be ok... Although they have a full charge cycle, I will have random time intervals. electronics.stackexchange.com/q/157069/62210 \$\endgroup\$ – MadHatter Oct 12 '15 at 18:19
  • \$\begingroup\$ Also looks like here it is OK, interesting that everywhere else on the web people seem to say avoid trickle charging... electronics.stackexchange.com/q/156981/62210 \$\endgroup\$ – MadHatter Oct 12 '15 at 18:23
  • \$\begingroup\$ what about temperature? I think Li-ion are less suitable for hot environments. Apart from that they should be a no brainer, especially for the 'memory effect' thing \$\endgroup\$ – Vladimir Cravero Oct 12 '15 at 18:39
  • \$\begingroup\$ So Vlad, your saying the Li-ion is a no brainier? It could experience temperatures up-to ~120F and down to ~-10F. As for life, If I get 1 to 2 years out of the devices battery's, that would be fine. \$\endgroup\$ – MadHatter Oct 12 '15 at 19:09
  • \$\begingroup\$ 50°C is ok, -20°C is less ok. Perhaps you can try to fit your device in an insulated contraption so that it heats itself? A constant 10 or even 20 delta T with ambient would be ok \$\endgroup\$ – Vladimir Cravero Oct 12 '15 at 20:55
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To my knowlegde Li-ion cells handle incomplete charging cycles very well. If you're sure to be able to provide comfortable temperature for the cells (0-40C or 30-100F), there is no reason to expect them to have a short battery life. Li-ion cells wear out quickly at higher temperatures, and should not be charged when cold (although discharge is OK).

Ni-MH batteries have a broader temperature range, but don't like to be recharged without a near full discharge first.

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  • \$\begingroup\$ That's precisley what my comment was about. I'm quite sure that there's an ideal charge level to store Li-ion batteries, something like 70%. If op can keep the charge around that level he might be able to extend nominal battery life. \$\endgroup\$ – Vladimir Cravero Oct 12 '15 at 18:40
  • \$\begingroup\$ Good point about the charge level. My ThinkPad charges the battery to 50% if I choose the "Extend battery life" power profile. I don't think there is a bing difference between 50 and 70%. \$\endgroup\$ – Dmitry Grigoryev Oct 12 '15 at 18:44

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