I thought so, but was just double checking.
That little piece of paper could be installed in the float 5 MM too high or low and throw off readings by 0.015.
So it is comparable to itself for future readings, but not necessarily to other hydrometers and no necessarily representative of actual SG.
So when you get the pendant, and force 14.4v to be held for longer, you can see if SG rises further, or is already at its maximum.
But since charging will warm up electrolyte, and that specific hydrometer has no indicator of electrolyte temperature, readings can appear to have stopped rising on the float, but if compensated for rising temps, can still be responding to the charging current.
When i take readings I make a chart with 6 cells 12v battery, note the date, the external temperature of the middle of the top of the battery, the SG reading on the float for that cell, the + or - number the OTC's thermometer tells me to add or subtract, and a estimation of how many MM below the hanging arms in the cells that the electrolyte level resides.
When electrolyte levels drop to nearer the tops of the plates, the Sg will read higher when fully charged.
After refilling the cells to a mm or 2 below the hanging arms in each cell, the SG readings will read very low until recharged again, and they will still read lower than before refilling.
Never add water, unless plates are exposed, when the battery is less than fully charged. If you do add water to the correct level when less than fully charged, and then charge it fully, it will likely burp some acid out of the cells and then still appear overfilled.
Voltage under load after a refilling, drops faster and is a bit alarming. Expect to see this if you watch the voltmeter often during discharge
However after refilling the acid is weaker and less corrosive to the plates, and the lesser voltages are nothing to be concerned about.
In the beginning, the batteries will not use much water. As their cycles accumulate, water use accelerates and the level must be checked more often.
The rate at which the battery uses water indicates 2 things, the time spent at or close to Absorption voltage where bubbling and offgassing occurs, and when under the same recharge regimen, when water usage accellerates and this rate of water loss increases then increases further, that the end is approaching.
it is too easy to say I check it every 3 months and it is always fine and does not need much, but at some point it will require watering every month, and if you go 3 months at that point, the plates will be exposed, and refilling at that point, is too little too late.
Once the plates become exposed on an older battery, the battery is basically done for, with little chance of restoring it to usable capacity. If it happens sooner in the battery's lifespan, refilling can allow it to still perform adequately.
I basically had 2 sets of battery's lives about 2/3 the way through, terminated at that point as I did not notice the accelerated water usage until it was too late. After refilling, even an aggressive equalization charge had no effect. Voltage tanked during discharge to alarming levels and I was buying new batteries shortly after.
These were 12v batteries. 6v GC batteries have more electrolyte over the tops of the plates, and are also much more likely to recover from such abuse, and require less time at absorption voltages to fully charge.
So the hydrometer can tell you how long absorption voltage needs to be held, so you do not have to hold them up there longer than needed, which causes positive plate shedding and more water usage.
The PD gives you the option of holding 14.4v for as long as needed, and ending 14.4v when needed too.
Do note the voltage at which the PD9245 maxes out. it is supposed to be 14.4v, but the unit I tested went upto 14.56v, and 13.6v normal mode was actually 13.73v, and 13.2v storage mode was actually 13.34v.
US battery wants a float voltage of 13.06v at 77F so the PD9245 is a little high for long term storage floating.
Pretty much impossible to find an affordable charger which meets manufacturer specs perfectly.
That 23$ power supply I've linked in the past, and do not recommend for novices, can hold an exact voltage, such as 13.06v, if dialed in to do so when not attached to the battery(s), and then connected. The danger with this cheapowatt power supply is when higher voltages are chosen and hooked to a depleted battery. and this is why it cannot be recommended.
This is the product I specifically do not recommend:
http://www.amazon.com/gp/product/B0...d_t=201&pf_rd_p=1944687542&pf_rd_i=B00ENFBXQS
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27939135/srt/pa/pging/1.cfm
The Megawatt power supplies are more expensive but have protections against overloading which deleted batteries will do:
http://www.12voltpowersupplies.us/
I wound up with a MeanWell RSP-500-15 which will supply 40 amps at any voltage from 13.12v to 19.23volts. I love this power supply. Ultimate manual control.