Understanding amp hours and lithium batteries

[Porkchopexpress]

While planning my electric power usage in a truck camper, I'm trying to wrap my head around how the tech specs translate to real world use. For example, the lithium battery in the camper will be a 100 ah 12v LiFePO4 deep cycle battery. When I compare the amp hours to the battery i use to charge my phone when I travel, (Anker Powercore 20,100mah) the specs don't seem that impressive. The Anker costs about $50 and I get 20 ah of power. If I was to add a second battle born battery to my camper, it would cost about $900 for 100 ah of power. Why is there such a price discrepancy? And why not supplement your camper battery with several Ankor Powercores for your portable devices for more cost effective power storage?

Thank you!

 

[john61ct]

Amp hours Ah are the best measure of capacity and usage over time

when the voltage is known and constant for comparisons.

But they are meaningless otherwise.

The industry is **very** deceptive about those overpriced portable powerpaks, often taking the **per cell** voltage rather than pack voltage to grossly inflate numbers.

A standard for say 12V nominal at 13.8V actual is very helpful.

Or converting to Watt hours Wh, but that is not precise.

Really when comparing different storage devices or even loads, you need to use the same coulomb counting wattmeter and actually measure to really know what's going on.

 

[john61ct]

So, that Anker pack may well have 3.7V cells, so their "20Ah" might be only 74Wh.

While 100Ah at 13.8V is 1380Ah, likely 20x as much usable energy.

Speaking of which, a lead battery at 100Ah is only 50Ah usable because regularly going under 50% you might only get 100 cycles or less.

While the LFP could in theory go to 5000+ cycles well treated, so going down to 15% SoC is not "too abusive"

so call that 85Ah usable energy (*13.8V = 1173Wh)

Those tiny power packs are very poor value, except for temporarily extending you phone / tablet runtime, say while hiking.

For solar only living off grid with a fridge/freezer, fans, lighting, maybe a full laptop,

300-400Ah usable at 12Vnominal is pretty normal, especially in cloudy weather far from the equator.

 

[Alloy]

For a direct comparison convert everything to watt/hours

mAh to Watt-hours (Wh) conversion calculator

Milliamp-hours (mAh) to Watt-hours (Wh) conversion calculator.

www.rapidtables.com

Amp Hour to Watt Hour Conversion Calculator - ElectricScooterParts.com

Online calculator for converting Amp hours Ah to Watt hours Wh.

electricscooterparts.com

 

[DaveInDenver]

Or converting to Watt hours Wh, but that is not precise.

Really when comparing different storage devices or even loads, you need to use the same coulomb counting wattmeter and actually measure to really know what's going on.

This is the fundamental to the O.P.'s original question.

A 20 A-hr Anker pack is nominally 3.7V, thus 3.7V x 20 A-hr = 74 W-hr

The 100 A-hr BattleBorn is nominally 13.8V, thus 13.8V x 100 A-hr = 1,380 W-hr

Just comparing 1,380 / 74 = 18.6 times the stored energy. If the Anker is $50 x 18.6 = $932. So forgetting any details about what or how much you can do with each or relative value the Anker and the BattleBorn value roughly balances out simply on a Dollar per W-hr basis.

You could in theory scale up with a ton of Anker USB packs but you will pay about $900 no matter what since you'd need approximately 20 of them to get the same run time on your fridge as the one BattleBorn battery.

 

[Alloy]

This is the fundamental to the O.P.'s original question.

A 20 A-hr Anker pack is nominally 3.7V, thus 3.7V x 20 A-hr = 74 W-hr

The 100 A-hr BattleBorn is nominally 13.8V, thus 13.8V x 100 A-hr = 1,380 W-hr

Just comparing 1,380 / 74 = 18.6 times the stored energy. If the Anker is $50 x 18.6 = $932. So forgetting any details about what or how much you can do with each or relative value the Anker and the BattleBorn value roughly balances out simply on a Dollar per W-hr basis.

You could in theory scale up with a ton of Anker USB packs but you will pay about $900 no matter what since you'd need approximately 20 of them to get the same run time on your fridge as the one BattleBorn battery.

....I can see this thread progressing to the size of alternator (3.8V or 12V ) needed to charge 20 Anker batteries

 

[john61ct]

The properly sized House bank gets recharged

off solar if stationary

opportunistic draws off the alternator (via DC-DC) **if** driving anyway

or maybe an inverter genset + mains charger

or mains directly when at a powered site overnight.


Then the little toy powerbanks that fit in your pocket get secondarily charged at the same time

or off the House bank when no charge source is active

just like phones / tablets or a laptop battery does.

 

[DaveInDenver]

....I can see this thread progressing to the size of alternator (3.8V or 12V ) needed to charge 20 Anker batteries

"Owner of an overland® camper tries paralleling 20 USB charge packs to run his laptop and cell booster working off grid for a week."

 

[Porkchopexpress]

Yeah, I guess you don't want to cheap out on lithium.
Another dumb question that seems hard to find a strait answer with search engines, will your truck camper battery slowly charge off the vehicle if connected to the trailer 7 way connector plug? I understand the wires are a thin gauge and to get a useful charge you need to add a dc to dc charger and thicker wiring and a disconnect but will the batteries charge at all from the 7 way?

 

[john61ct]

Volts are volts amps are amps

each battery has its specs for determining 100% Full

measure at the battery post to see how much voltage drop / current wastage

Again, a coulomb counting wattmeter can just sit and monitor flow rate.

Just know, a deep cycling lead bank takes 7+ hours to refill, even at high voltage, no matter how many Amps you start off with.

And failing to get to that 100% Full point at least 2-3x per week will cause early death of the bank.

Huge advantages of LFP right there. . .

 

[Alloy]

Yeah, I guess you don't want to cheap out on lithium.
Another dumb question that seems hard to find a strait answer with search engines, will your truck camper battery slowly charge off the vehicle if connected to the trailer 7 way connector plug? I understand the wires are a thin gauge and to get a useful charge you need to add a dc to dc charger and thicker wiring and a disconnect but will the batteries charge at all from the 7 way?

Will the water from one tank will flow into another tank......yes it will if one tank is higher (voltage) than the other. The speed at which the tank fills is controlled the size of the hose (wire).

 

[vomhorizon]

Yeah, I guess you don't want to cheap out on lithium.
Another dumb question that seems hard to find a strait answer with search engines, will your truck camper battery slowly charge off the vehicle if connected to the trailer 7 way connector plug? I understand the wires are a thin gauge and to get a useful charge you need to add a dc to dc charger and thicker wiring and a disconnect but will the batteries charge at all from the 7 way?

Yes it will slow charge though you naturally want to do that with a LA battery. You probably do not want to straight charge a drop-in LiFePO4 battery from the alternator because it could damage it, and the connections and wire unless you really know what you are doing. Have some sort of management system or DC-DC handle that for you. Red-Arc make a low power (12A) DC-DC charger for trailers that allows you to use the 7 way connector plug without having to run a dedicated connection from the starter battery to the back to handle a much more powerful charging system.

12A Trailer Battery Charger

Charge your trailer batteries with this 12amp dump trailer charger from REDARC.

redarcelectronics.com

 

[Rando]

This is the fundamental to the O.P.'s original question.

A 20 A-hr Anker pack is nominally 3.7V, thus 3.7V x 20 A-hr = 74 W-hr

The 100 A-hr BattleBorn is nominally 13.8V, thus 13.8V x 100 A-hr = 1,380 W-hr

Just comparing 1,380 / 74 = 18.6 times the stored energy. If the Anker is $50 x 18.6 = $932. So forgetting any details about what or how much you can do with each or relative value the Anker and the BattleBorn value roughly balances out simply on a Dollar per W-hr basis.

You could in theory scale up with a ton of Anker USB packs but you will pay about $900 no matter what since you'd need approximately 20 of them to get the same run time on your fridge as the one BattleBorn battery.

This whole Amp hour thing is a weird quirk of the battery industry and makes very little sense. It is crazy that you would try to represent energy storage (which is what we are after) with a Amp hours. Really it should be in Joules, but Watt hours at least makes physical sense. Seeing this is the USA, I guess I should just be happy that it is not in BTU.

 

[DaveInDenver]

This whole Amp hour thing is a weird quirk of the battery industry and makes very little sense. It is crazy that you would try to represent energy storage (which is what we are after) with a Amp hours. Really it should be in Joules, but Watt hours at least makes physical sense. Seeing this is the USA, I guess I should just be happy that it is not in BTU.

I've never really thought about it but you're right. Maybe it's because of the use of ammeters and thus Coulomb counting to stick with it as a base unit?

 

[Rando]

Coulomb counting can just as easily produce Wh by multiplying by the voltage at each sample. Most Coulomb counters will also display in Wh. Maybe back in the day when everything was lead acid batteries, and everything ran of linear regulators which 'conserve' current, then Ah was at least kind of defensible. Now with (almost) everything running of switch mode power supplies which 'conserve' power and all sorts of battery chemistries with different nominal voltages, Ah make even less sense.