I remember from chemistry that you always read volume in a graduated cylinder at the bottom of the meniscus. But what about the hydrometer? Just got to thinking about it today when I was checking the SG before charging. Depending where you take the reading could easily result in a 10 point variation.

Doesn't seem to matter where you measure that one give or take a half inch the battery just isn't going to make it. :B

1.2825 or there abouts.Make sure no bubbles stick to float. Lesser states of charge seem to have more bubbles stick to float.Make sure glass tube is mostly vertical with minimal contact between float and glass sides.If checking while charging, note that inner cells will be warmer than outer cells and temperature compensate accordingly.Give the thermometer a while to respond to the electrolyte temperature, and cool ambient temps will throw off readings.If the battery has not moved and not been charged for a while, the electrolyte can be stratified, with the dense acid on the bottom. This will throw off readings. So some agitation, or holding it at gassing voltages should mix it up for a more accurate reading.Quick, get a charging source on that poor battery or I will report you for batterycide!! :)

Actually the batteries were fully charged before applying a 40A load for 90 minutes. That's when I took the reading. Recharging right now!

In this case read the bottom of the meniscus. The top of the meniscus is just surface tension of the glass and the liquid and is to be ignored.

I know I'll get cr@p from the battery crowd here, but this "unclear" line has bothered me for years both on battery hydrometers, as well as the one I use floating in my salt reef tanks. There is friction glass to glass in the hydrometer tube as well as water creep on the probe, and the same water "creep" on my floating tank probe. In the tank I can look at it from below the water line and above and interpret two different readings.In the salt tank I cured this issue with a Refractometer. For the batteries I just bought a HydroVolt and used it on my T-145's over the weekend. It tracks my glass tube hydrometer exactly without the tapping of bubbles and rattling around to zero out the glass on glass friction with a repeatable reading. It's simply a better mouse trap and no glass to break. Read the full .PDF sheet on it.

Properly reading a battery hydrometer | Good Sam Community

30 Replies

SCVJeff
Explorer
Feb 19, 2016
pianotuna wrote:
Hi Jeff,

Do you see the same sort of heat issue when using the inverter side of the Magnum?
No, but I rarely have occasion to pull anywhere near that current kind of current. It lives 99% of its life around 20A (DC draw) with an occasional 180A Popcorn run and morning coffee @~60A. But neither are sustained.
pianotuna
Nomad III
Feb 18, 2016
Hi Jeff,

Do you see the same sort of heat issue when using the inverter side of the Magnum?
SCVJeff
Explorer
Feb 18, 2016
full_mosey wrote:
MEXICOWANDERER wrote:
The "lost" amp hour capacity in an absorbed glass mat battery is exactly why the battery can survive "100%" discharges, resist freezing while barely having a charge and a a whole host of other attributes that separates the battery from flooded lead acid batteries. I had the old Trace 2500SB charging at it's maximum rated 120-amperes at 12-volts plenty of times without smelling like Mount Krakatoa. I wonder what's different about the Magnum?

Yeah, what's different compared to my MS 1012 100W/50A Magnum that BULK charged for 50+minutes into a 270AH AGM bank full bore with nary a smell.

Now what did happen is the thermal overload kicked in which lowered the rate to 30A for a while. For another 25+min the BULK stage continued and the rate alternated between 50 and 30A.

HTH;
John
This one makes twice that current and it's failsafe is around 240F IIRC. One difference in venting is that the heat exhaust blows into the basement/ cable raceway under the floor and there's a vent under the bed that opens to both spaces. If that wasn't there I would never know about the smell. I'm also hyper sensitive to smells like that. I can smell a smoked 1/10W resistor in a rack room on the other side of the building :(

(Edit: iPad spelling)
SCVJeff
Explorer
Feb 18, 2016
MEXICOWANDERER wrote:
The "lost" amp hour capacity in an absorbed glass mat battery is exactly why the battery can survive "100%" discharges, resist freezing while barely having a charge and a a whole host of other attributes that separates the battery from flooded lead acid batteries. I had the old Trace 2500SB charging at it's maximum rated 120-amperes at 12-volts plenty of times without smelling like Mount Krakatoa. I wonder what's different about the Magnum?
Dunno what the difference is, but Magnum swapped it out once already as I was bumping up against the transformer foldback temp. The 1st one they were convinced that the varnish dip had air bubbles around the windings and causing heat problems. This one is WAY better and doesn't dip into failsafe, but it still gets hot
full_mosey
Explorer
Feb 18, 2016
MEXICOWANDERER wrote:
The "lost" amp hour capacity in an absorbed glass mat battery is exactly why the battery can survive "100%" discharges, resist freezing while barely having a charge and a a whole host of other attributes that separates the battery from flooded lead acid batteries. I had the old Trace 2500SB charging at it's maximum rated 120-amperes at 12-volts plenty of times without smelling like Mount Krakatoa. I wonder what's different about the Magnum?

Yeah, what's different compared to my MS 1012 100W/50A Magnum that BULK charged for 50+minutes into a 270AH AGM bank full bore with nary a smell.

Now what did happen is the thermal overload kicked in which lowered the rate to 30A for a while. For another 25+min the BULK stage continued and the rate alternated between 50 and 30A.

HTH;
John
MEXICOWANDERER
Explorer
Feb 18, 2016
The "lost" amp hour capacity in an absorbed glass mat battery is exactly why the battery can survive "100%" discharges, resist freezing while barely having a charge and a a whole host of other attributes that separates the battery from flooded lead acid batteries. I had the old Trace 2500SB charging at it's maximum rated 120-amperes at 12-volts plenty of times without smelling like Mount Krakatoa. I wonder what's different about the Magnum?
SCVJeff
Explorer
Feb 18, 2016
pianotuna wrote:
Hi Jeff,

A footprint that does 115 amp-hours for flooded yields about 105 amp-hours in AGM. However the AGM does charge faster and voltage support is somewhat better. The path forward may be to LI chemistries and right now cycle life cost is pretty much identical to AGM. Flooded is still the price king.

SCVJeff wrote:
As for AGM's I don't think I can get the same capacity in the same footprint.
im not worried as much about price (within reason) as capacity since a 2AM lights out is pretty standard. The Magnum alone can deliver about 105A but that can take the transformer above 200F pretty quickly before I start smelling varnish. But as Niner can attest, access to these batteries for fluid check requires removal of the front two to get to the rear two, that's why he's trying to talk me into AGM :)
pianotuna
Nomad III
Feb 18, 2016
Hi Jeff,

A footprint that does 115 amp-hours for flooded yields about 105 amp-hours in AGM. However the AGM does charge faster and voltage support is somewhat better. The path forward may be to LI chemistries and right now cycle life cost is pretty much identical to AGM. Flooded is still the price king.

SCVJeff wrote:
As for AGM's I don't think I can get the same capacity in the same footprint.
SCVJeff
Explorer
Feb 18, 2016
The scope Don has shown above can be found all over eBay from under $20 to over $90 for what looks like the same unit.. They can sometimes be hard to read but once you get the right light the line is unmistakable.

As for AGM's I don't think I can get the same capacity in the same footprint.
pianotuna
Nomad III
Feb 17, 2016
Refractometer: