Building box to contain four 12v 15ah AGM batteries.

I am building a box to contain four 12v 15ah AMG batteries to power a small kids motorbike (48v altogether). Space is tight and I would ideally like to fit the batteries side by side flush up against each other with no movement. Should this be OK or is it absolutely necessary to have some padding between each one.
Someone might suggest using a lithium battery but for a number of reasons I have chosen to use the AMG's.
Thanks in advance

With your normal AGM case, they're beefy enough to just be strapped together.

Thanks for your answer Voltron. J

Ya know... "AGM batteries" makes me think "stone age" in electric traction terms? So. Just curious why would someone EVen consider spending so much more for "Absorbed Glass Matt" than lithium-based chemistries? Just look at your Atomic Table, for example:


... Where Pb (plumbum="Latin" for lead) is sorta far down the list? Great chemistry as a starter battery... but pretty horrible for "deep cycle"...Notice where lithium sits ("Li") on the table?

No padding needed if the movement is minimal. If it makes it easier to secure the whole pack, you can use some silicone, hot glue, or whatever to connect the cells into a solid block.

AMG doesn't have free hanging plates, so there isn't much vibration risk. the only real danger is if they can wiggle around, they may slowly rub a hole in the case. So being strapped down without padding is usually better.

^^ ... and add lots of weight, requiring more energy to accelerate and go against gravity ("up hills"). ... AND start sulfating as soon as they're "less than full". OTOH, used/worn-out SLA makes handy door stoppers. (I just ran out of doors to wedge open.)

Thanks for all your answers and advice. There are a few reasons I want to use agm batteries over lithium . One being the expense, a good quality 48v 15ah lithium battery however efficient is very costly . Secondly the small motorbike they will power using a hub motor originally had an engine weighing over 25kg and so the weight would be a good substitute for that when the batteries are placed in the same area (16kgs roughly). Also to be honest I have a bit of a worry about the safety of lithium , 9 times out of ten or more they should be fine but have heard of fires etc .
We have an old single seater golf buggy for the kids to race around on that runs off two 12v lead acid batteries and to be honest the batteries are fairly old but they seem to go on and on powering that.
Any thought still appreciated though . Thanks

Keep in mind that you aren't getting nearly 15Ah from 15Ah lead batteries. More like half that much, if you want them to last more than a handful of cycles. So a lithium battery of 8ah represents at least as much practical capacity as a lead battery of 15Ah.

When you take into account the cycle life of lithium versus lead, it's usually much cheaper per ride to use the better battery. If you must cheap out, hoverboard packs are a way better bargain than lead bricks.

Thanks Chalo.
If I did go for a 48v lithium and to keep the cost down went for 10 ah would,in your opinion, this have enough "torque or whoomph" to drive a small motorbike with a 48v 800w brushless hub motor. Altogether the motorbike and rider etc would weigh no more than about 65-70kg. You are swaying my opinion !

Whether a given lithium pack can support the load your motor puts on it is dependent on both the specific cells and the BMS. You want both those current limits to be greater than the current rating of your motor controller. 800W electrical is about 17A at 48V. An 800W nominal system could in some cases draw twice that much current at peak load. Some batteries will do it but others won't.

Hobby lithium cobalt pouch packs will put out lots of current from a cheap, lightweight package, but they have a sketchy safety record. They don't come with BMS, either. 18650 cell based packs are easy to live with, but some don't provide as much current as your system might demand.

Engineered lithium battery packs won't exhibit much voltage sag within the discharge limit set by the BMS. SLA based systems often sag enough to attenuate the current demanded by the load, causing the battery to serve as a sort of passive power limiter.

Consider that saving roughly 50 pounds of battery weight will reduce the amount of battery power you need to get the job done.

Well. a 15ah AGM weighs about 10 pounds.. so 4 of them is 40 lbs. Its going to take a heck of a lithium battery to save 50 lbs off of that...

My Hawker Odyssey batteries had similar capacity and weighed about 60 pounds for four of them with minimal mountings, as I recall.

$249 for a battery that will outlast at least 3 sets of AGM($399).

https://www.aliexpress.com/store/product/US-EU-No-Tax-Electric-Bike-48V-12Ah-battery-with-54-6v-2A-charger-for-li/1178407_32757820761.html?spm=2114.12010612.0.0.3cff63c29DrKO2

3 pack of 15ah AGM on amazon is $117.. not $399... or maybe you meant 3 3 packs... either way, around kids, lead still has a place when performance isn't an issue, given lithiums sensitivity to over discharge and overcurrent damage.

Yes, lithium can be destroyed through abuse, neglect, or technical failure. Lead quickly becomes destroyed though routine normal use.