Battery condition indicator

A battery condition readout device is disclosed. A series of slides of varying densities float or sink according to the amount of charge. An optical system permits slide position to be seen at a point external to the battery.

BACKGROUND AND OBJECTIVES OF THE INVENTION 
The present invention relates to a device which is mounted in a storage 
battery to measure electrolyte concentration and also indicate low 
electrolyte level. The invention will provide a motorist or mechanic with 
a quick visual check of the electrical charge and will warn of low liquid 
level in the battery. In this way any deterioration caused by aging or a 
faulty charging system can be readily detected and remedied. 
The invention utilizes differentially-weighted, floatable slides and an 
optical system through which the position of the slides can be viewed from 
a point outside the battery. When the battery is fully charged, all the 
slides float. This corresponds to maximum concentration and density of the 
battery's electrolyte. A caption on the slide nearest the optical system 
appears in a window mounted in the top surface of the battery. As the 
battery discharges, the density of the electrolyte decreases; the 
differentially-weighted slides sink in succession. The captions on these 
slides appear one by one in the window. When the battery is completely 
discharged, the last slide--which has a density slightly less than that of 
water--remains floating and its caption indicates the discharge state of 
the battery. Should the electrolyte evaporate or leak to a dangerously low 
level, however, all the slides will sink; this exposes a low level caption 
placed on a hitherto occluded wall of the slide container. 
It is one objective of the present invention to indicate in words the 
condition of charge of a storage battery. 
It is a second objective of the present invention to utilize slides which 
float or sink according to the condition of the electrolyte and according 
to its level. 
It is a further objective of the present invention to provide a simple and 
accurate method for economically producing the slides required in the 
construction. 
These and other objectives are met by the invention to be explained in the 
appended description and the drawings. 
DESCRIPTION OF THE PRIOR ART 
It has been the previous practice to use an adaptation of the floating ball 
hydrometer in conjunction with a light conducting tube installed in place 
of one of the fill caps of a storage battery. If the battery is charged, a 
brightly colored ball can be seen at the end of the tube. The ball's 
density is adjusted so that it floats when the battery is fully charged. 
This is the working principle of U.S. Pat. Nos. 3,093,516, 3,218,857, 
3,895,964, 3,915,753 and 4,308,817. Full charge or full level are the only 
conditions indicated. Intermediate readings which could be used for 
diagnosis are not provided. The device described by Miyagawa (U.S. Pat. 
No. 4,074,025) uses swinging vanes to indicate an intermediate charge but 
only color changes are displayed. The user must retain the meanings of the 
various colors in memory or refer to a chart. This is a difficult task 
when a large number of color schemes are employed by various battery 
manufacturers. The present invention identifies battery condition by name 
so that changes can be directly noted. 
In the prior art the density of floating body must be calibrated--a time 
consuming operation. Adjustment of slide density in the present invention 
can be done quickly and accurately in a large scale manufacturing 
operation.

DESCRIPTION OF THE INVENTION 
A preferred embodiment of the invention, as shown in FIGS. 1 and 2, is made 
up of the rectangular, transparent body 1 to which is attached the slide 
container 2. Body 1 is polished flat on its top surface and is formed and 
polished at a 45 degree angle at its bottom. Surface 7 is preferably 
mirrored to enhance reflection and to prevent refractive loss of light 
when body 2 is immersed in battery electrolyte. 
The slides 3, 4 and 5 are of successively increasing densities and can move 
vertically along grooves formed inside container 2. The transparent body 1 
is sealed into plug 8 which is threaded to fit a standard battery fill 
port. Plug 8 may also be provided with friction-fit surfaces to slide into 
a standard friction-fit port used in some battery types. If the invention 
is to be incorporated during the manufacture of the battery, it can be 
provided with a specially drilled port. 
Further details of the invention can be explained with reference to FIG. 2. 
The container 2 is open at the top and closed at the bottom by plate 10. 
Holes 9 in these plates permit circulation of battery electrolyte into and 
out of container 2 and also allow the escape of gas bubbles. 
The slides 3, 4 and 5 are of increasing densities so that they will float 
in increasing concentrations of the electrolyte. Tabs 14 on the slides 
contact the grooves 6 so that rubbing friction during ascent and descent 
is minimized. Each slide bears a caption--3L, 4L, 5L, etc. which indicates 
the amount of chrage the battery must have inorder for that particular 
slide to float. When a slide is floating, its caption is reflected by the 
mirrored surface 7 to the viewing surface 15. A coasting 16 protects the 
mirror from contact with the electrolyte. When the battery is fully 
charged, all the slides float. In this case, the caption of the slide 
nearest the mirror is seen at the viewing surface 15. A suitable caption 
for slide 5 might be "Max" or "Chrgde". When the battery is partially 
discharged, slide 5 sinks but the others remain floating. The second 
slide's caption 4L is now visible in the viewing surface 15. A suitable 
caption for slide 4 might be "Fair", "Med" or "OK". If the battery charge 
decreases still further, slide 4 sinks but slide 3 remains floating. 
Caption 3L might read "Dischrgd", "NG" or "RPLC". Slide 3 has a density 
slightly less than that of water and will remain floating at any charge. 
If all the slides drop to the bottom of container 2--as would be the case 
if the electrolyte level were to drop sufficiently--the caption 12L placed 
on the rear wall of the container 2 would appear on the surface 15. A 
suitable caption of 12L might be "Refill" or "Lo Lvl". The above 
description is based on the use of three floats; more or fewer floats can 
be incorporated in the design to be adaptable to a particular battery and 
its application. 
An accurate and low cost method of slide construction is shown in FIG. 3. 
Each slide is made up of a lower layer c, a transparent upper layer a and 
a perforated, transparent center layer b. The materials used may be 
transparent plastic or glass. The density may be adjusted by variations in 
the number and diameter of the holes 18. The layers can be cemented 
together or, with certain materials, pressure-sealed together. The 
captions, e.g. 5L, are imprinted on the bottom layer c so that they are 
protected from exposure to battery electrolyte by the lamination process. 
Protection for the caption 12L is provided by applying an acid resistant 
coating. In large scale production of the slides, the layers a and c can 
be stamped or injection molded. The center layer b can be produced by a 
hole punch and a stock of various density center layers produced. The 
relation between slide density and the number and diameter of holes is 
given by: 
##EQU1## 
where D.sub.s =density of the assembled slide 
n=number of holes 
d=diameter of each hole 
l=length of slide 
w=width of slide 
D.sub.m =density of slide construction material. 
A cross bar 20 retains the slides at the top of their travel when the 
battery is fully charged.