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I'm looking at using a stock Sparkfun Li-po/Li-ion Battery Babysitter to charge an array of four 18650 Li-ion rechargeable cells (Panasonic) in parallel, keeping the pack voltage at 3.7 V.

I chose the charger because it has excellent monitoring and control on-board. I read the data sheet for the Texas Instruments charge controller and it had the needed protection for the unprotected batteries (under-voltage, over-voltage), with the over-current protection provided by a simple fast-blow fuse.

The only issue is that the charger only runs at 1.5 A max current. Considering that the battery array is capable of taking more than four times that rate, is there going to be an issue charging so slowly?

I've seen Sparkfun recommend this charger for their 3.7 V Li-po pack that uses three 18650 cells, so I figured it would be fine and just charge very (very) slowly. If it's necessary, I suppose I could wire up two chargers and split the cells between them, but I don't mind the slow charging rate if it won't hurt the batteries.

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    \$\begingroup\$ Unless you charger has a timeout "feature", there should ne no problems. \$\endgroup\$
    – winny
    Jul 13, 2017 at 5:35
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    \$\begingroup\$ The only very minor point that you might want to consider when slow charging like this is that those chargers usually shut off at c/10 or in your case 1500mA/10 or 150 mA. For a single cell this is totally fine, but when spread over four cells it is really closer to 40 mA/cell (37.5 to be exact). This is fine, but means your cells will be very very full. And the fuller you stuff your cells the faster they start to lose capacity and more likely to burn if abused. But a minor point. \$\endgroup\$
    – Filek
    Jul 13, 2017 at 6:21
  • \$\begingroup\$ Ah, very good point, I will check into the documentation for the controller. \$\endgroup\$
    – Will
    Jul 13, 2017 at 17:01
  • \$\begingroup\$ An older Lithium battery is 4.2V when fully charged. 3.7V is half a full charge and is the storage or selling voltage. A LifeP04 battery is newer and is about 3.6V when fully charged. \$\endgroup\$
    – Audioguru
    Nov 17, 2022 at 0:43

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There is no minimum charging current for Li-ion batteries. You'll be fine. Just don't leave the charger connected for a prolonged time.

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