# Gary Ayton's camping and photography wiki

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australia:battery_capacity

# battery capacities compared, how much do you need?

## Introduction

• 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 level of discharge
• 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

• 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

## How long will your appliance run?

• this is easy to ascertain:
• duration in hours = Usable power capacity in Watt-Hours / Power usage in Watts(W)
• a 240V AC microwave runs at 1200W
• a small 12V car heater demister fan runs at ~150W
• a laptop generally runs at 65W
• an 12V electric blanket generally run at 20-45W (max 75W)
• 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)

## How many times can it fully re-charge your smartphone?

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

## How long will it take to fully re-charge your smartphone?

• 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

## Some comparisons

• 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)
• standard 3.7V 2700mAh lithium rechargable battery will give a usable power capacity of 10Wh (100% DoD)
• 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