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When I go hiking, I only recharge my phone to about 80% from my backup supply because I know it gets harder and harder to push more energy into a battery the closer it gets to full capacity. So I am roughly assuming I could charge my phone a few times to 70%, versus 1 charge to 100%. (The higher the voltage in the battery the slower and less efficient recharging seems to be. Even how superchargers for Tesla can charge to 80% almost instantly, but takes considerably longer to reach 100%)

I was wondering if anyone knows what that graph looks like. Total energy input vs percent charged.

**I know it depends on battery type and recharge rate and all that, but generally speaking, they should have a similar graph.

It won't be linear, but how about exponential? logarithmic? or is it just the inverse and derivative of discharge?
enter image description here

Can I charge to 70% two times vs one charge to 100%? Any rule of thumb to follow while on my hikes??

My efforts to search haven't been very rewarding, so I figured I'd ask.

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  • \$\begingroup\$ 50%. But you can put it in more than twice as fast becaues you don't have to use the increasingly slow CV stage. You don't gain anything in terms of energy use, but it's faster. \$\endgroup\$
    – user16324
    Commented Jun 25, 2018 at 10:27

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The batteries you're talking about are lithium ion. They have specific charging procedure where you put constant current until 80% and then you do constant voltage from there to 100%. That's why it takes longer above 80%. Constant voltage means there's less and less potential difference between the resting battery voltage and the charging voltage so it'll get slower and slower. Up to 80% it's basically linear. After that it'd be effectively asymptotic since the charge voltage is effectively the same as the final resting battery voltage.

You could charge your batteries differently than this industry standard, but if you did so, you may blow up the batteries.

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  • \$\begingroup\$ the graph shows the charge rate slowing when it reaches 90% charged (after about 2 hours of charging). \$\endgroup\$
    – Jasen Слава Україні
    Commented Jun 25, 2018 at 4:48
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This is not for LiPo used in phones rather lead acid for PV systems.

The optimal charge voltage for a 12V battery is typically 14.2V and this is also just above the threshold for a rapid rise in loss of energy charge efficiency.

This may suggest you consider reducing the LiPo max charge voltage from 4.2V to 3.9V which Battery University also indicates as the optimal for long term energy unit life but a reduction certain loss in mWh capacity. (-20%?)

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