User Tools

Site Tools


Words of Wisdom:

Over many years of capacity testing hundreds and hundreds of batteries, flooded, GEL and AGM I have yet to see a lead acid battery that could delivers its full storage potential at anything less than 0.75%1) in tail current at absorption voltage. MaineSail2)

Battery murder

Battery murder (or Batterycide) is the murder of batteries by newbs (new users), poor quality chargers, etc. The term is commonly used by SternWake: “my goal here is to prevent batterycide.”3)

It is so common for new RVers to wreck their first set of house batteries that some recommend using cheap wally world batteries as sacrificial lambs to the learning process.4) As the RVers learns more and gets charging set up correctly they would invest in better quality batteries and have them last several years.

murdering flooded lead-acid

Flooded lead-acid (FLA) batteries are the most resillient to mistreatment but they too can be killed.

  • leaving them at partial state of charge, resulting in irreversible sulfation5) Fully charging each day is optimal. Fully charging almost every day is acceptable.
  • not charging at manufacturer-recommended Absorption voltage (Vabs) to reverse normally-occurring (“soft”) sulfation. This is most commonly caused by isolator-only charging since the house bank is being charged at 6) alternator voltage.
    Less commonly, Solar-only charging can cause this problem if the battery capacity is too great for the solar output.7)
  • not holding Vabs for sufficient duration so that absorption current drops to manufacturer-recommended levels. Generator- or DC-DC charging can cause this unless the charger runs the necessary number of hours it takes to complete Absorption.
  • discharging too deeply. Discharge with lead-chemistries is typically limited to 50% depth of discharge as a compromise between cycle life and bank size.
  • allowing the cells to get low on distilled water. Check them 1x/month or so until you learn their personality.
  • exposing them to heat, as in an engine bay

murdering AGM

AGM have benefits but are easier to murder.

  • the lead-acid list above8)
  • overvoltage
    • Incorrect Absorption setpoints. AGM is commonly Absorped at ⇐ 14.4v while FLA is commonly Absorped higher (at 14.7v-14.8v). Check your manufacturer's recommendation and do not exceed it. Overvoltage causes irrepairable damage by outgassing, and AGM cannot be topped off again like FLA.
    • Equalization. Do not equalize AGM!9).
  • Low current charging. Cheap AGM require C/5 current minimum in Bulk, and expensive ones require C/3.

murdering lithium

  • overvoltage. 13.8v is a safe upper limit without BMS and will charge the bank completely. Some experienced folk use slightly higher voltages for faster charging but it must be terminated quickly as the bank approaches 100% state of charge. Exception: Lithium banks with BMS typically overcharge intentionally to balance cells. The overcharge is consumed by resistors and does not actually go into the cell.
  • long periods of 100% state of charge; cease all charging at 100% and only charge that high if you know some loads will be applied immediately.
    • IF you're storing the van or know you're not going to be using the batteries for more than a couple days, it's strongly recommended to leave lithium batteries at 50-80% SOC. Lithium chemistries do not care about partial state of charge, and actually prefer it..
  • exposure to high heat
  • attempting to charge at below freezing
  • poor quality BMS
  • high [dis]charge rates without BMS
electrical/batterycide.txt · Last modified: 2024/06/15 21:48 by frater_secessus