House Batteries Interstate L-16HCL

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JJSchmidt1946

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I have a 2013 Monaco Monarch class A Motorhome. Equipment includes a regular two door home electric refrigerator powered by a 2000 watt inverter and 4 interstate 6 volt L-16 HCL wet cell Batteries. We dry camp infrequently but often stop for overnights at Wal-Mart or Roadside Rests when traveling. I have had a couple of times when the low power alarm has gone off and had to start the gen set after hours to keep the batteries up and the fridge operating.

I am thinking about changing out the house batteries and finding a lot of confusing information from the several manufacturers regarding replacement battery capacities. My existing batteries, Interstate L-16HCL indicates Capacity-20: 420 Reserve Cap-25: 940 Reserve Cap-75: 250
I looked at an MK Battery today 8L16-DEKA which gives the following specifications Capacity at C/100: 420Ah Capacity at C/20: 370Ah

Can someone out there help me understand the numbers and what they mean? Seems the manufactures give similar but not the same specifications and list them differently making it difficult for me to determine if one battery is comparable to the other. Thank you
 
There's one number that's common between both batteries - the amount of Amp-Hours the battery can deliver over a 20 hour constant discharge.  That's Capacity -20 for the Interstate, Capacity at C/20 for the Deka.

The Interstate L-16HCL is rated at 420 amp-hours, the Deka is rated at 370 Amp-Hours.  In other words, the Deka battery stores 13% less power than the Interstate.

The rest of the numbers are just different ways of measuring the battery capacity.

Interstate rates their batteries using Reserve Capacity, which is an easier test to administer than the 20 hour constant discharge test.  Reserve Capacity places a 25 amp (or 75 amp) constant discharge on the battery, and measures how many minutes it takes the battery voltage to fall to 10.5 volts.  That's the Reserve-Cap 25: and Reserve-Cap 75: numbers.

The 20 hour Amp-Hour test is more complicated to perform, you have to estimate how many Amp-Hours the battery can deliver, then test it for that length of time.  If you guessed wrong, you have to do the test again at a different Amperage, until it takes exactly 20 hours to go from full charge to discharged.

Complicating the issue is batteries deliver more power when they're slowly discharged than they do when they are discharged more rapidly.  It's called the Peukert effect after the guy who discovered it, and is why you can't directly convert Reserve Capacity into Amp-Hours unless they both happen to use the same discharge current.
 
The key thing here is to make an apples-to-apples comparison, either amp-hours or RC (Reserve Capacity). As Lou explained, amp-hours have to be on the same capacity (hours) basis, e.g. C-20 or C-100. C-20 is the standard measurement for Amp-Hours, but advertisers like to use C-100 or C-75 because the resulting numbers are higher.  Likewise, the RC value for 25A discharge rate will be higher than the RC for 75 A.  Don't get fooled by AH or RC numbers using a different basis for the measurement.  And if they battery specs do not quote either a C20 (20 hour) AH value or an RC @ 25A value, skip it and go to another brand.

A quick sanity check is battery weight. It takes a certain amount of lead plates to produce a given quantity of amp-hours or RC, so two batteries that produce the same amounts will invariably weight the same, within 1 lb.
 
420 AH is decent battery capacity, but it's not really surprising that you occasionally run low on power during an overnight stay unless you actively conserve power. Use of much lighting, or an inverter, or the furnace fan can chew through a lot of amps. You didn't mention at what level the "low power" alarms goes off, but it could be as high as 12.0v (about 50% discharge on the batteries). I know our coach (390 AH battery capacity) could reach the 12.0v level early in the evening and we often ran the genset for 30-40 minutes once or even twice during the evening, depending on how much power we were using.
 
As Lou said the C/20 or c-20 rating is the one we go by.. You want lots of Amp Hours at C/20
(THis means it takes 20 hours to discharge that many amp hours)

THere are several numbers that are important.. C/20 is how long the batteries last between recharges (The bigger the AH number after the longer.  also teh longer to recharge.

Height, Width, Depth, Pounds.. Those matter too but only when it comes to "Will it fit and can I lift it"

DEEP CYCLE is important as well  Note DEEP CYCLE is not MARINE/deep cycle or other "Multi-Use' it means DEEP CYCLE

Finally voltage  you need 12 volts. you can get ther ein one piece. 2, 3 or 6 but you need 12 volts

When you put batteries IN SERIES add Voltage and all batteries must be the same age, type, size, and so on,
IN parallel add amp hours and you can mix if you wish.


One last caution: Some companies use different rating means. IE: Wal*Mart rates how long the battery can provide ONE AMP. this means they get much larger numbers.. Beweare of those. For any give size battery. any other than OPTIMA will be nearly identical. OPTIMA is far less (Ab out 60% of the rest) due to the cylinderical (Sprial) Design.
 
You cant really determine anything about the batteries not holding through the night unless you know if they were actually fully charged. A good fully charged battery will not only be about 12.6 or 12.7 volts but the specific gravity must be up. That's a fully charged battery. You also cant make valid comparisons unless you know how many amp hours you are removing from the battery. I used to run on four GC2 and always made it through the night when running the house furnace, 42" led tv, led lights etc but the only way to really compare is to know the amp numbers.  I would say that there was no way that those four GC2 were going to give up 200 AH (1/2 their rating) and be above 12 volts.  Check the SG.
 
You have 800+ AH of battery.  There should be no reason with good batteries why you can't go all night with the fridge running and still have decent capacity left in the battery. 

As QZ said you must know if your batteries are fully charged, of if not, just how far the batteries are discharged.

Some things to check:
-- have you checked the water level in the battery?
-- stop by an auto parts store or Amazon and buy a battery hydrometer line this: https://www.amazon.com/Golf-Cycle-Battery-Hydrometer-Tester/dp/B00NCWAPEY/ref=sr_1_4?ie=UTF8&qid=1509737214&sr=8-4&keywords=battery+hydrometer&dpID=31XaeN2nXeL&preST=_SY300_QL70_&dpSrc=srch
-- use the hydrometer to check the specific gravity of each cell.  Here are instructions on houw to use the hydrometer: http://all-about-lead-acid-batteries.capnfatz.com/all-about-lead-acid-batteries/lead-acid-battery-maintenance/how-to-check-a-battery-with-a-hydrometer/

Your batteries, if original to the RV they are 5 years old.  If they have not been very well maintained, they may be weak or have a bad cell. 
-- If the RV was in storage over the winter and the batteries were allowed to deeply discharge that could be the cause. 
-- If the RV was in storage over the winter and there was to high a float voltage that could be the cause.
-- If the water level was allowed to get so low as to expose the plates, that could be the cause.

 
Also be aware that you are dealing with sulfuric acid. It will eat everything it gets on. It's best to wear goggles and even have some water handy for eye flushing when working with batteries. Batteries also produce hydrogen gas when charging and a spark near the top of the battery can turn it into a bomb.
 
QZ said:
Also be aware that you are dealing with sulfuric acid. It will eat everything it gets on. It's best to wear goggles and even have some water handy for eye flushing when working with batteries. Batteries also produce hydrogen gas when charging and a spark near the top of the battery can turn it into a bomb.

If you have one of those polyester leisure suits from the '80s, now is the time to break it out. Sulfuric acid loves to eat cotton, so don't dress in tee,s and Levi's, but polyester holds up very well to acid. I was the maintenance supervisor in a sulfuric acid plant.
 
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