battery capacities compared, how much do you need?

see also:

• 12V batteries and battery boxes
• solar power for camping
• camping off-grid - power, batteries, solar, fridges
• lithium jump start batteries and other jump starters
• looking after your batteries
• USB cables, connectors and protocols

• manufacturers often make it hard to directly compared battery capacity as they often rate them in various measures such as Ah, mWh, etc, so this page is to make this more simple for you.
• There are several aspects that need to be compared:
  • maximum capacity of the battery
    • this is best measured as Watt-hours (Wh)
  • usable capacity in Wh
    • recommended maximum depth of discharge (DoD)
      • lead acid batteries should only be discharged to about 50% of their capacity to avoid permanent damage to the battery
      • LiFePO4 batteries can be discharged down to 0% charge but the more this happens, the less lifetime cycles you will get
    • depth of discharge lifetime cycles (DoD)
      • for LiFePO4 batteries, this is often rated at number of lifetime cycles of 80% DoD and this tends to range from 1000-4000 cycles depending upon the design and quality of the battery
    • how many DoD cycles has been done already
      • there is a gradual decline in maximal capacity over usage time of hundreds of cycles

• Watt-hours is a unit of total energy
  • either capacity of a battery, or the amount used, or needing to be used for a given task
• using watt-hours as a measure instead of amp-hours (Ah) means that you can better equate batteries of different voltages and you have a universal measure of how long a battery will last given use of a appliance of a known amount of Watts independent of the voltage
• Watt-hours (Wh) = Amp-hours (Ah) x Voltage = average watts used per hour x number of hours
  • ie. a 20W light bulb running for 1 hour uses 20Wh of energy
  • ie. a 12V LiFePO4 battery with a capacity of 100Ah and nominal voltage of 12.8V has an energy capacity of 1280Wh (= 12.8V x 100Ah) and this would allow a 20W device to run for 64 hours (= 1280Wh / 20W)
• 1Wh = 3600J = 860.4 calories = 3.4 BTU
• by definition, it takes 1 calorie to heat 1g (=1mL) of water by 1degC, thus to heat 500mL water from 15degC to boiling (100degC) should require 42,500 calories = 49Wh (in reality due to less than 100% efficiency, an electric kettle will actually use around 57Wh)
• by definition, BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit

• this is easy to ascertain:
  • duration in hours = Usable power capacity in Watt-Hours / Power usage in Watts(W)
  • a portable 2000W AC single induction stove will generally cycle with peaks of 1200W when at settings of 1200W or lower but average output will be determined by the power setting with the lowest usually being 200W and usually needing at least 600W for cooking, and will be 2000W at max. power output
  • most 240V AC microwave runs at 1000-1100W
  • a small 12V car heater demister fan runs at ~150W
  • a laptop generally runs at 65W
  • a 12V electric blanket generally runs at 20-45W (some have a max. 75W)
  • a 35L Dometic car fridge generally runs at 20-25W with careful use (pre-cooled and packed with already cold food and drinks)
  • smaller USB powered heating pads ran at 8.4W
• if you are using amps and amp hours both in the same voltage:
  • duration in hours = Usable current capacity in Amp-Hours / Current usage in Amps (A)

• this is easy to ascertain:
  • number of times of full re-charge = usable power capacity of battery (Wh) / power capacity of smartphone battery (Wh)

• this is relatively easy to ascertain:
  • re-charge time in hours = power capacity of smartphone battery (Wh) / recharge supply power (W)
• recharge supply power (W):
  • this is dependent mainly upon the charging adapter
  • the 5.2V USB-A charge adapters were only 5W and then you could get the 10W “iPad” chargers and even 12W chargers
  • standard USB-C chargers are around 18-20W with 9V, 2.2A outputs
  • USB-C Power Delivery (PD) Fast Charge adapters for smartphones designed for PD Fast Charge (models iPhone 8 and later)
    • 29-96W chargers are available

• 100Ah LiFePO4 battery will give a usable power capacity of 1200Wh (100% DoD)
• 100Ah Lead Acid battery will give a usable power capacity of ~600Wh (50% DoD)
• 3.7V 20000mAh power bank / lithium 12V car jump starter will give a usable power capacity of 54Wh (100% DoD)
• 3.7V lithium ion cylindrical rechargeable batteries
  • 3.7V 21700 4000mAh 14.8Wh batteries are generally industrial use not civilian use - use those with protection boards to reduce risk of short-circuit
  • 3.7V 18650 2700-3500mAh 10-13Wh are commonly used in many rechargeable devices
• 3.2V LiFePO4 cylindrical rechargeable batteries
  • 18650 size are usually 1600mAh = 5.1Wh
• iPhone batteries (3.83V):
  • 13: 3227mAH = 12.4Wh
  • 13 Pro: 3095mAh = 11.9Wh
  • 13 Pro Max: 4352mAh = 16.7Wh
  • 12 and 13 Mini: ~2400mAh
  • 12 and 12Pro: 2815mAH = 10.8Wh
  • 12 Pro Max: 3687mAh = 14.1Wh
  • iPhone SE 2020: 1821mAH = 7Wh
• headphones generally have 2Wh batteries

• these are mainly designed to provide power for smartphones, laptops, other USB devices
• BLUETTI X20 Power Bank for Laptop
  • 2025 model based on LiFePO4 batteries with a BMS and gives over 2500 cycles of charge
  • 153.5Wh (12Ah at 12.8V) with built-in 45dB fan to avoid over-heating
  • can be carried in backpack (but not on planes)
  • can connect 4 devices as once to max total 288W output
    • DC output with 12 adapters compatible with over 90% of laptops on the market 20V / 8A = 160W max
    • 100W PD3.0 USB-C (20V 5A 100W bidirectional charging, fully recharge in 2hrs) - 5V/ 9V / 12V / 15V / 20VDC 3A; 20VDC 5A; eMarker chip built-in / PD3.0 / QC3.0+ / SCP / FCP / AFC
    • 18W QC3.0 USB-A - 3A 5V; 2A 9V; 1.5A 12V;
    • 10.5W 2.1A 5V USB-A
  • 205x205x77mm; 2.3kg; 0°C to 40°C charging temp; $AU299
  • https://www.bluettipower.com.au/products/x20-portable-power-bank
• “3.6V” powerbanks
  • these are lower capacity and measured in mAh at 3.6V (they often don't give the Wh capacity which is what you need to compare capacities with 12V power banks)
  • these may not be able to power higher powered laptops which need more than 100W but will re-charge them via USB-C if they have USB-C recharging
  • TSA airplane max battery capacities were 100Wh for these devices - check the latest restrictions as these change for each carrier
  • you may need an optional high powered 100W USB-C charging base for fast charging of the power bank
  • Anker Laptop 165W Power Bank
    • 25000mAh at 3.6V = 90Wh
    • three 100W USB-C ports plus one 33W USB-A port allowing max 165W total output; retractable cables;
    • 157x54x49mm; 595g
    • https://www.anker.com/au/products/a1695 $AU180
  • Anker A1340 Laptop 250W Power Bank
    • 27650mAh at 3.6V = 99.54Wh
    • two 140W PD3.1 USB-C ports plus one 65W IQ USB-A port allowing max 250W total output;
    • 170W output PD USB-C using dual USB-C outputs
    • when charging two separate devices max is 140W for one USB-C and then 100W for the other USB-C or 65W for a USB-A
    • when charging three separate devices max is 140W for one USB-C and then 92W for the other USB-C and 18W for a USB-A
    • Bluetooth smart app;
    • https://www.anker.com/au/products/a1340-250w-power-bank $AU240