Battery Cycles Logic

Finhobbyist

Finhobbyist

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Ok, so lately you keep on hearing that a deep cycle gel battery wont last during the current loadshedding stages, as it is pushed into too many charging cycles.
How does a car battery then last for three years, as a new charging cycle starts with every turn of the key??
 
Finhobbyist said:
Ok, so lately you keep on hearing that a deep cycle gel battery wont last during the current loadshedding stages, as it is pushed into too many charging cycles.
How does a car battery then last for three years, as a new charging cycle starts with every turn of the key??
Click to expand...
Because the start/charge cycle you are talking about uses a tiny part of the battery's capacity. It's not a full cycle.
 
One cycle is a complete discharge to 0 and then back to full.

So 100 -> 0 -> 100 would be one cycle.
100 -> 50 ->100 -> 50 -> 100 would also be one cycle.

In the case of a car, you're only using battery power to start the car. When the car is running, the alternator keeps the battery fully charged...
 
Finhobbyist said:
Ok, so lately you keep on hearing that a deep cycle gel battery wont last during the current loadshedding stages, as it is pushed into too many charging cycles.
How does a car battery then last for three years, as a new charging cycle starts with every turn of the key??
Click to expand...
Because car batteries are being used for what they were designed for. LS Deep Cycle batteries in a UPS application is a different story.
 
Mike Hoxbig said:
One cycle is a complete discharge to 0 and then back to full.

So 100 -> 0 -> 100 would be one cycle.
100 -> 50 ->100 -> 50 -> 100 would also be one cycle.

In the case of a car, you're only using battery power to start the car. When the car is running, the alternator keeps the battery fully charged...
Click to expand...
That would be more for a lithium battery, sadly on a LA batter 100 - 50 would basically almost be an entire cycle anyway.
 
When you start a car, you would only use around 5ish% of the battery to start the engine, meanwhile in a UPS situation, you are regularly draining it far beyond that
 
If you let your car stand a lot and the battery runs flat you are also going to buy a lot of batteries.
 
The key is depth of discharge. The number of cycles the battery tolerates is highly dependent on DoD. And it's completely different for lithium vs. lead acid.

Lithium might be rated for say 3000 cycles at 80% DoD i.e. 100% -> 20% and back.

Lead acid will be killed very fast that way. Some good charts at https://batteriesonline.co.za/depth-of-discharge-dod/

TT-DOD-768x484.jpg

So for lead acid you have to massively oversize the battery if you want it to last in cyclic use. If you look at the chart you see it's also non-linear. So doing 25% DoD instead of 50% more than doubles cycle life.

I have a car battery powering a router UPS and it's still strong after 3 years, and that's after it did 3 years in an actual car.

DoD in that case is about 5% given 2-hour loadshedding.
 
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