Cycles Schmycles

[GallenH]

I need some education here! Batteries (old-fashioned AAs, cell phone, RV) state they're good for a number of recharge cycles. What does this mean? For example, my iPhone sits on a recharger base. If I take it off and make a call and then replace it, is it entering a new "cycle?" IOW: is it better for battery health to let it deplete, off the charger, and only charge it periodically when it gets down to, say, 30%??

What's the best strategy here for battery life (both cellphone and RV)?

[rowiebowie]

Sorry, can't help. The more I learn the less I know.

[GallenH]

Originally Posted by rowiebowie

The more I learn the less I know.

By your other posts and what you've done on your RV.........I'd say that's definitely not true. Cheers.

[Davydd]

From what I can find out, a cycle is a full discharge. So if your lithium batteries are assumed 80% efficient (as mine are since the bottom 20% is locked out) then you can discharge 10% eight times for a full cycle. I typically while on the road discharge 25% daily. When in storage, less than 5%. So typically 100 days on the road for a year that's maybe 34 cycles. In storage 265 days then that is lets say 54 cycles. Maybe 88 cycles per year. Lithium ion batteries are probably good for 2,000 cycles to where you lose 20% capacity. Anyway, theoretically they could be good for over 20 years. But there may be several abuses in that time like cold temperature, high temperature effects and discharging to depletion. All I can say is no one has a 20 year old lithium ion battery van to verify. Mine is 4 years old and still very effective.

My batteries have never gone below 41 deg. but once when I accidentally turned to heater off and I have gotten to 100F ambient about two or three times. I've never fully discharged below 50% but a few times and only once to 20% cutoff in testing. I've never had a van more than 5 years (3 so far) so don't worry about it.

With an 800ah battery bank I have plenty of reserve since I don't or seldom use air conditioning. That helps because I never stress my batteries in percentage of cycle discharge. If I had 200ah lithium batteries I would probably cycle daily on the road. But heck, if you did that, that is still 5-1/2 years if I was full-time of more profligate use of battery than AGMs. Profligate means no propane all electric use.

[RossWilliams]

There is no standard for "cycles". In the case of your Iphone, Apple apparently considers one cycle to be a full discharge and recharge (or equivalent partial discharges and recharges).

For RV lead acid batteries, AGM or flooded, the relationship between the number of cycles you will get and the depth of discharge is not linear. Two 40% discharges are not equivalent to one 80% discharge. Some battery manufacturers have charts showing the number of cycles at different depths of discharge for their specific batteries. While there are differences, they will all show that, in general, you will get longer battery life, more cycles and more total capacity by limiting the depth of discharge. Which is to say, two 40% discharges will get you longer life than discharging once to 80%.

[W9TR]

I think limiting abuse is the best way to extend battery life.
What defines abuse depends on the battery chemistry.

For lead-acid batteries;
The big issue is sulfation. By limiting discharge to 50% of the battery's amp-hour rating and not leaving the battery in a discharges state for very long will maximize life. Avoid full charge/discharge cycles and recharge as quickly as possible after a deep discharge. Float charging these batteries to 100% will keep them in top shape. Partial discharge - charge cycles will maximize life. Heat is the enemy of lead-acid batteries, AGM or flooded.

For Lithium chemistry batteries;
A different beast but some of the same principles apply with some significant differences. Usually, a combination of several factors increases battery life. For increased cycle life:

Use partial-discharge cycles. Using only 20% or 30% of the battery capacity before recharging will extend cycle life considerably.

Avoid charging to 100% capacity. Keeping your iPhone on a charge cradle all the time will reduce battery life. Charging to 80% or 90% will increase cycle life and service life at the expense of reduced battery capacity.

Limiting temperature extremes extends battery life, especially prohibiting charging below 0°C.

High charge and discharge currents reduce cycle life. Some chemistries are more suited for higher currents such as Li-ion phosphate. High currents place excessive stress on the battery. But you want to run your microwave so there's that. Just do it.

Very deep discharges will quickly, permanently damage a Li-ion battery. Most Li-ion batteries have protection circuitry within their battery packs that open the battery connection if the battery capacity drops below 20%.

I'm an electrical engineer by trade. I designs batteries into safety critical alarm systems. I hope this info has been helpful.

I've got a lot of experience with lead-acid batteries in various RV's and vehicles. I've managed to keep our boat battery alive for 10 years so far using the principles outlined above. I've designed a lot of smaller Lithium Ion batteries in products that are still humming 15 years on. But I haven't used them in a vehicle application yet.

Tom

[gregmchugh]

Lots of discussion about this here in the past for AGM batteries that indicate that for discharges up to 80% there is no major reduction in battery life. The battery has the capability to provide a certain number of total AH over the life of the battery pretty much independent of the depth of discharge for any cycle. The 50% discharge limit rule does not seem to provide any major improvement in the total AH provided by the battery over its life.

[RossWilliams]

I doubt AGM deep cycle batteries perform differently in RV's than they do everywhere else. They are called deep cycle for a reason, they can be drawn down further than a standard flooded lead acid battery. As I understand it from multiple sources, they still exhibit the same characteristic of reduced cycle life as the depth of discharge increases, but it is much less pronounced. You don't want to discharge a standard flooded lead acid battery below 50%. With deep cycle batteries, an average 50% depth of discharge is a guideline for optimum sizing of your battery bank but you can draw them down to 80% occasionally.

By contrast AH ratings are, by definition, determined using a constant current. They vary widely depending on how large that current is. For the usual AH rating given for comparison of AGM batteries' the capacity is determined using a current of .05 C, which translates to fully discharging the battery in 20 hours. Your actual capacity can be much larger if you discharge more slowly with a lower current and much less if you discharge faster with a higher current. Some battery manufacturers provide multiple AH ratings for different currents which allows their customers to better evaluate batteries for their intended use.

In short, there are a lot of different factors that determine how much electricity you will get from your batteries both in the short run and over their life. But in most cases the heavier the use, the less capacity you will have.

[W9TR]

Correct. With AGM, the time the battery is left in a discharged state is important. You can discharge deeply if you charge back up to 100% quickly. The sulfation process that limits AGM battery life is dependent on the battery’s state of charge and time. So leaving an AGM at 20% for a long time is more harmful than a number of shorter discharge/charge cycles.

[GallenH]

Thanks to all who responded. I got some very useful information....the education I was looking for. Cheers.