What to look for when selecting a lithium-ion battery charger IC

Question

I'm looking into battery charging ICs for a 3.7 V lithium-ion battery, and want to make sure I understand the criteria involved in searching for such an IC.

The obvious one is to make sure the IC is designed with the battery's chemistry in mind (bad idea to charge a Li-ion battery with a lead-acid battery charger), but do I sacrifice anything by choosing an IC that can charge multiple types of battery chemistry?

In other words, if I'm already going with lithium ion, would choosing an IC that can also charge lithium polymer be a compromise in any way? If it was, would the compromise be worth it or not?

I've also heard accounts that it's best to match charging current to the mAh of the battery (e.g. 1000 mAh battery should get a 1000 mA charging current). However, other reading indicates that this is incorrect, and that doing so only speeds up the charging time (and can also produce more heat, to the point of burning out the IC if you aren't careful). Can anyone confirm one way or another?

Next, I want to confirm something regarding the specified voltage of the battery. Is it better to choose a charger IC based on the battery's maximum voltage or its nominal voltage? Is one or the other safer and/or better for long-term battery life?

Lastly, and this is a little unrelated to the criteria, but if I chose a battery whose current capacity was way in excess of what I need (e.g. 2600 mAh when the attached device only draws 5 mA and only expected to be powered for 1/2 hours a day), would that be considered wasteful?

Answer 1

bad idea to charge a Li-ion battery with a lead-acid battery charger

Not really. Both lead acid and Li-ion use a CCCV charging profile. (NiCd and NiMH don't.) The difference between lead acid and Li-ion is just the top voltage. Also, a lead acid charger should be temperature compensated, and a Li-ion charger doesn't need that. Also, many lead acid chargers have two different Constant Voltage stages. While better lead acid chargers end charge if a time-out is reached, better Li-ion chargers end when the current drops below 0.1 C. But, fundamentally, they're generally the same basic charger. Many applications switch from lead acid to Li-ion batteries and keep on using the same charger: forklifts, golf carts, and cell-phone towers.

The main reason we may not use a lead acid charger is not because it's for lead acid, it's because its voltage cannot be adapted for a given Li-ion battery.

do I sacrifice anything by choosing an IC that can charge multiple types of battery chemistry?

No, not really.

e.g. 1000mAh battery should get a 1000mA charging current

Not really. In the absence of a spec sheet, the default charging current should be 0.5 C. E.g., a 1000 mAh cell should get a 500 mA charging current.

Is it better to choose a charger IC based on the battery's maximum voltage or its nominal voltage?

They are two different ways of specifying the same thing. You can see a charger "for 3.6 V cells" or a "4.2 V" charger. They're the same. One charger tells you that its for cells that have a nominal voltage of 3.6 V (implying that the maximum voltage is 4.2 V). The other charger tells you that at 4.2 V it switches to constant voltage mode (implying that it's for 3.6 V nominal voltage cells).

Is one or the other safer and/or better for long-term battery life?

They are both the same. It's only how they're labeled that is different.

a battery whose current capacity

It's not "current capacity". It's just "capacity".

would that be considered wasteful?

No. Nothing is being wasted. You're just getting a longer discharge time before you need to recharge.