In regard to charging Li-ion - Lipo battery packs:
Previously, I have always "recommended" - "highly recommended", the implementation of a PCB\PCM\BMS, recent trials with a dedicated Li-ion charger, seems to prove it, an unnecessary item! ... ?(Tenergy 25.9v 2A charger - <$30 each, shipped, if buy 2.)
After I noted, that my homemade packs, were maintaining decent equalization of voltage between cells, others chimed in, agreeing that they have been recharging, without any form of balancing - equalization circuit. 2 claimed, that "good" cells, with varying degrees of monitoring, required no balancing circuit! Even after 100+ cycles!
The typical PCB\PCM\BMS monitors against over-charging pack, as well as of individual cells or banks of cells.
Secondary function prevents the over-discharge of pack, or cells.
The "optional" function is a balancing, or equalization, function.
This is normally accomplished by a "bleeding down", of the higher voltaged cells.
The normal equalization circuit is rated at between 5-10% of the charging voltage.
My iMax B8 balancing charger, charges at, up to, 7 amps, but the balancing circuit operates at a maximum 0.3 amps.
A PCB rated at 30 amps "balances" at a mere 60mA .06 amps. Sadly, this looks to be typical - meaning that "balancing", to be effective must be used on cells of "near balanced" state, or would require an extreme "equalization time".
After I tested and evaluated my recycled cells I took the acceptable, applied an initial balancing, assembled them into packs, and have been running-testing them for hundreds of miles, with a dozen+ recharges!
Packs have been tested for equalization after discharge and after recharge.
Both packs, Li-ion & Lipo, maintain within 1/100th volt of "full charge" 4.18v. (1 variance, might have been a mere few thousandths volt.)
Typically, I discharged to the 3.7- 3.8v range, where equalization was to, a less impressive, but very acceptable, 2/100th volt.
Packs seem "stable", very similar to my "recycled" packs, that I have been running for, 3 years, and thousands & thousands of miles.
As previously mentioned, I monitor cell & pack voltage, pre- & post-charge.
While I have used an odometer - in conjunction with the oem voltage leds, I would recommend a voltage meter-low voltage alarm.
Cheap multi-featured one available, from China.
Nice little volt meter for 8 cells, or less!
Monitors, and displays pack voltage, then of each bank.
Low-voltage alarm is programmable from 2.7v to 3.8v, in 1/10v increments. Meter & Low Voltage Alarm
More than 8S?
Take 2 they're small! And cheap! $6.29
Extension cable, from balance plug to voltmeter-alarm can place unit on your bars, for constant monitoring!