Minimum battery charge - 10%

[ianganderton]

I was watching a video from Pacific Yacht Systems on another thread and the guy (Jeff) mentions that not charging to a minimum of 10% of the battery rating can damage the battery

I hadn’t heard of this before. Does anyone have any info they can share on this?

Is it just lead acid or lithium too?

What is the 10% calculated on?

if the battery was a 12V 100Ah AGM would this mean minimum charge current should be 10A?

 

[John Frum]

Link please.

 

[RCinFLA]

Needs clarification.

Could interpret as at least three different meanings. My first guess would be charging current in AH capacity amps. That would be the least incorrect of my three interpretations.

Never trust drunken sailors on a Saturday night. Just party with them.

 

[DASH]

Check with the battery manufacturer. There are different requirements for different battery chemistries. There can even be differences on recommended charging, discharging etc with the same battery chemistry but different manufacturers.

 

[ianganderton]

Link please.

it’s in here.

Video is quite long and I’m on my phone so difficult to find exact location. I’ll dig it out later

 

[ianganderton]

@21:54 ?


cant remember exact words but basically saying below 10% charge rate causes decreased capacity over time. Pretty sure it’s agm related but not sure as it wasn’t mentioned more specifically hence the question

 

[ianganderton]

Title should include the word rate, sorry

 

[Dzl]

Pacific Yacht systems almost never directly talks about or considers Lifepo4 in their videos. I have learned a lot from Jeff and PYS, but not regarding lithium. From what I've seen I wouldn't consider him especially knowledgeable about the chemistry (not that he is ignorant of it, but it seems he has much more expertise with lead acid and mostly ignores lifepo4 in his videos/lectures).

 

[John Frum]

Not going to watch the video but he seems to be talking about charge rates as a percentage of c rate.
Looks like it only applies to lead acid.

 

[RCinFLA]

For boats, there are a lot of occasions you do not have time to wait for an extended low amperage charge time. What this 10% comment means is have enough charger capabilty to charge batteries by at least 10% of their amp-hr (AH ) capacity rate in amps (was my original first guess).

Probably a good portion of his audience have no idea what the batteries in their boat Amp-Hour capacity is. What they bought fit in the existing battery box.

Just about all lead-acid can handle up to 15% AH charge rate, AGM's can take a bit higher, and LiFePO4 50%, some even higher. You don't have to do the high rate but if you want to get things going as quickly as possible have the rate available.

In a pinch, you can push lead-acid with even more recharge current, 20-25%, when lead-acid battery is at less then 70% state of charge but need to back it down when they get greater then about 13.5 vdc for 12v lead-acid which is where electrolyte starts splitting up more water into hydrogen and oxygen gas and battery really starts bubbling at higher rate. For sealed, maintance free type you really have to be careful to prevent too much gas buildup.

 

[ianganderton]

My understanding from the video was that charging regularly with less than 10% reduced their capacity. Would this maybe through sulphation?

he comments on boats typically leaving the ‘factory’ with alternators rated at 10% of the fitted battery and folks not realising that when batteries get upgraded to higher ratings then altentors do too

I hadn’t heard of these minimums before

 

[RCinFLA]

It is important to periodically keep a lead-acid fully charged to prevent discharged lead-sulfate from crystalizing which will not recharge.

It is not important that it be done above 10% AH charging rate other then it takes more time to achieve full charge at lower rate. If some sulfation has occurred, higher charge rate may dislodge it and at least free the plate surface from blockage caused by the hard sulphate crystals. Some chargers have 'equalization' mode which is a controlled overcharge to perform this function. Equalization requires more current and runs the charge voltage over 15vdc per 12v battery. It is stressful to battery and sealed types should not be subjected to an equalization cycle as it build up too much gas pressure. Equalization also consumes a lot of electrolyte water and generates a lot of hydrogen gas which might not be a good thing in a confined space.

How often 'periodic' is different for true deep cycle battery versus starter or dual purpose lead acid batteries. For starter or dual purpose once a month should minimize sulfate crystal build up. Deep cycle is built with antimony alloy plates which has a greater rate of self discharge then calcium alloy starter-dual purpose batteries which have lower leakage current.

Many boaters use a 'battery tender' to float their batteries all the time at about 13.2 vdc.

I just realized that chart page could be terribly mis-interpreted. Leaving a lead acid at low level of state of charge would be very bad for battery. Its intentional meaning is charge rate in % of AH capacity in amps. 10% charge rate for 100 AH battery is 10 amps charge current.