This is another question regarding "
the popular $20 headlight" (someone added a post right after my question in
that thread without addressing my question
so I'm starting a new thread):
To prolong the battery lifespan, what's the best to use this light, if I have two battery packs 1 & 2 for the light?
a) charge 1 fully, use it half way, set it aside and use battery pack 2 from full charge until half way, then set 2 aside, use 1 (after fully charging it).... In other words, always use them from full charge to about half way, never use it all the way to totally discharged.
b) charge 1 fully and use it all the way to totally losing the charge, then use 2 (fully charged) until half full--meanwhile, charge 1 to about half full and keep it waiting---because I read that lithium battery should be kept partially charge when not in use. Then charge 1 fully before using it. In other words, always use each battery pack from full to no charge.
(Real experience should make more sense than theory
)
(btw for that damn tight connector, I have to use pliers to disconnect it after each ride
)
Personally I think you're over-emphasizing the importance of battery management, but since you did ask I can give you the best scenario for prolonging Li-ion battery life...first:
1) you need a charger that will allow you to set the maximum charge voltage ( a hobby charger will do this ). This will allow you to charge the battery to than less than it's normal peak voltage. For a normal 2S2P 4-cell set-up this is 8.4volts. What you want to do is charge the pack to 8 volts. This helps prevent premature aging of the cells. The down side to doing this is that it will shorten the run time of the battery by 20%.
2) ...then run the battery till it nears it's pre-set cutoff. Usually this is around 6 volts. The deeper you discharge a Li-ion battery the faster it will age. Best not to store a Li-ion battery fully charged as this also ages the battery faster. Store with less than a full charge. In a nutshell those are the technically facts.
Realistically doing all of what I just said would be a total PITA. If you bought cheap batteries charge them to normal peak voltage ( just before you ride ) and get whatever you can get out of them. Controlling all the aging factors of a battery is very hard to do. My best advise is: Buy the best quality batteries you can. Keep the battery away from extreme heat when storing. Buy a battery with a capacity that best suits your need. If you are into long epic type of riding a larger capacity battery is what you want.
All said, since you have two batteries I would suggest charging the batteries you want to use
( to full peak voltage ) just before going out. Then if you think you might ride long enough to need just a bit more run time, bring along the other battery and switch the first out when the indicator reaches red ( or if no indicator ) run the first battery till you think it is near shut-off voltage and then switch out batteries. At that point you run the second battery as long as it takes to get you out out of the woods. Keep the first battery as your reserve. If you have no voltage indicator on your lamp you will have to do a test discharge using your lamp at home so you know how much run time your battery/lamp will provide you during normal use. Just be sure to use a fan to cool the lamp if you do this.