question

klito avatar image
klito asked

Is keeping batteries fully charged good for battery life of a BMZ Z lion battery?

The configuration has 3xMultiplus+CERBO-GX+BMZ Z battery. As I use "virtual battery" from the grid operator, there is a smaller cost associated with storing the excess energy in the grid and using it when needed compared to the cost of storing the energy locally in the battery. The battery is thus in the system, at present, only to allow the Multiplus system to work. How should the system be configured to maximize battery life?

There is a "use battery with battery life" option in the ESS configuration. But this appears to be for situations when the battery is to be actively used as a source of energy.

Every KwH stored results in wear of the battery. On the other hand, keeping lion batteries fully charged seems to be discouraged in another post (https://community.victronenergy.com/questions/35861/is-it-good-for-the-batteries-to-keep-them-fully-ch.html). So what is the optimum state of charge? Should the battery be periodically discharged/recharged? What is the recommended period? I did not find any recommendation on this from the battery manufacturer.

Also, I am not sure how to configure the system. The Cerbo has a minimum SOC limit menu option but not a maximum one. Maybe preventing the full SOC could be achieved using the scheduled charge level menu option.

The questions are:

- What is the best option to ensure long term battery health of a Lion battery (BMZ) when the battery is needed only as a backup?

- How to configure CerboGX to achieve this?


battery chargingESSLithium Batteryess settingsbatterylife
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
Alexandra avatar image
Alexandra answered ·

@klito

If you look carefully at the graphs you will see the voltage rise and fall during use.

100% SOC is not a constant voltage especially if you are using ess. Not several things

1. Voltage drop in power assist with heavy loads.

2. Voltage rise to bulk during the day

3. Drop to float

4. Rebulk/absorption at certain intervals.

I can quite honestly say i have several 'keep batteries charged systems' and there is alot of movement in and out of the batteries anyway. So it is not like they are totally idle.

Fyi there is some new thinking having a storage voltage on LI systems now.

Your link to the other thread is the address of your own (this) post.

2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

klito avatar image klito commented ·

Hi,

Thanks for your reflections, yes, there is some constant charging and discharging. As I understand, this is a general feature of Victron systems.

The link to the other post is here: https://community.victronenergy.com/questions/35861/is-it-good-for-the-batteries-to-keep-them-fully-ch.html

One of the comments says that "in general, keeping the batteries under constant charge is not ideal."

Thanks also for the excellent pointer about the storage voltage. I found this post (https://electronics.stackexchange.com/questions/294842/is-it-better-to-keep-lion-battery-charge-on-the-lows-or-the-highs-for-battery-li), where the most voted answer recommends 60-70% capacity. I am not sure if this applies to BMZ battery chemistry. Anyway, it is unlikely that keeping batteries fully charged is the best option for battery life.

I would be interested in knowing more about the "storage voltage" function. Is it already available for LION batteries?

Given that the battery is the most expensive single part of many PV systems, I was wondering what options does the Victron ESS provide to optimize battery life in the long term. Is there an easy way to set the target SOC at 70% capacity in CERBO GX?

0 Likes 0 ·
Alexandra avatar image Alexandra ♦ klito commented ·
You would have to use node red.

Have you tried contacting BMZ for their official response to your question

Most batteries moving voltage between bulk and float is enough to not consider them as static or held at one SOC. So the point of keeping them charged is not keeping them in one place.

You would always have them optimised and at 100%.

Battery life in ess refers to battery storage, not to be mixed up with battery life/health. Battery health is a completely different topic and each manufacturer has a different way of evaluation.

Battery health is usually determined by

  • energy in and out.
  • How fast the energy is pulled in and pulled out. (C rating in use)
  • Operating temperatures

to name only a few.

0 Likes 0 ·